sound: rk29: pcm: fix bug on rockchip_pcm_enqueue

sound: rk29: pcm: fix bug on rockchip_pcm_enqueue

Fix this bug:
Unable to handle kernel paging request at virtual address 6b6b6b77
pgd = d41ec000
[6b6b6b77] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT
CPU: 0    Tainted: P             (3.0.8+ #250)
PC is at rockchip_pcm_enqueue+0x2c/0xec
LR is at rk29_audio_buffdone+0x58/0x84
pc : [<c0713094>]    lr : [<c071361c>]    psr: 80000193
sp : d0bfdcf8  ip : 00000001  fp : d51f5c44
r10: d0a2e414  r9 : 6b6b6b6b  r8 : 6b6b6b6b
r7 : 00000001  r6 : d53abc80  r5 : 6b6b6b6b  r4 : d0a983c0
r3 : 6b6b6b6b  r2 : d6d6d6d6  r1 : 0000001d  r0 : d53abc80

[<c0713094>] (rockchip_pcm_enqueue+0x2c/0xec) from [<c071361c>] (rk29_audio_buffdone+0x58/0x84)
[<c071361c>] (rk29_audio_buffdone+0x58/0x84) from [<c0447a50>] (rk29_pl330_rq+0x270/0x2d0)
[<c0447a50>] (rk29_pl330_rq+0x270/0x2d0) from [<c04438f4>] (pl330_update+0x374/0x438)
[<c04438f4>] (pl330_update+0x374/0x438) from [<c0446d3c>] (pl330_irq_handler+0xc/0x18)
[<c0446d3c>] (pl330_irq_handler+0xc/0x18) from [<c04960e0>] (handle_irq_event_percpu+0x30/0x174)
[<c04960e0>] (handle_irq_event_percpu+0x30/0x174) from [<c049627c>] (handle_irq_event+0x58/0x80)
[<c049627c>] (handle_irq_event+0x58/0x80) from [<c0498358>] (handle_fasteoi_irq+0xb4/0x108)
[<c0498358>] (handle_fasteoi_irq+0xb4/0x108) from [<c0495d70>] (generic_handle_irq+0x28/0x3c)
[<c0495d70>] (generic_handle_irq+0x28/0x3c) from [<c0433060>] (asm_do_IRQ+0x60/0x84)
[<c0433060>] (asm_do_IRQ+0x60/0x84) from [<c04384c4>] (__irq_svc+0x44/0xa0)
Exception stack(0xd0bfde10 to 0xd0bfde58)
de00:                                     00000001 00000108 00000002 00000000
de20: 00000013 d5028640 c0b0d32c d05e8808 d05e8800 d05e8808 c0b0d804 d0bfdeb8
de40: d4bd2400 d0bfde58 c0454ab4 c046ef54 40000013 ffffffff
[<c04384c4>] (__irq_svc+0x44/0xa0) from [<c046ef54>] (__queue_work+0x334/0x370)
[<c046ef54>] (__queue_work+0x334/0x370) from [<c046efdc>] (queue_work_on+0x2c/0x34)
[<c046efdc>] (queue_work_on+0x2c/0x34) from [<c046f024>] (queue_work+0x2c/0x54)
[<c046f024>] (queue_work+0x2c/0x54) from [<c047b214>] (__async_schedule+0x194/0x1b4)
[<c047b214>] (__async_schedule+0x194/0x1b4) from [<c070f118>] (dapm_power_widgets+0x334/0x3a4)
[<c070f118>] (dapm_power_widgets+0x334/0x3a4) from [<c070f234>] (snd_soc_dapm_stream_event+0xac/0xbc)
[<c070f234>] (snd_soc_dapm_stream_event+0xac/0xbc) from [<c070b3a0>] (soc_codec_close+0x164/0x178)
[<c070b3a0>] (soc_codec_close+0x164/0x178) from [<c07025a0>] (snd_pcm_release_substream+0x54/0xa4)
[<c07025a0>] (snd_pcm_release_substream+0x54/0xa4) from [<c0702618>] (snd_pcm_release+0x28/0x6c)
[<c0702618>] (snd_pcm_release+0x28/0x6c) from [<c04c8e50>] (fput+0x104/0x1f8)
[<c04c8e50>] (fput+0x104/0x1f8) from [<c04c5e60>] (filp_close+0x6c/0x78)
[<c04c5e60>] (filp_close+0x6c/0x78) from [<c04c5f30>] (sys_close+0xc4/0x124)
[<c04c5f30>] (sys_close+0xc4/0x124) from [<c0438940>] (ret_fast_syscall+0x0/0x30)

rk29_audio_buffdone call rockchip_pcm_enqueue, which access
rockchip_runtime_data *prtd, but prtd is freed on rockchip_pcm_close.