rk29: backlight: fix kernel BUG by double add_timer while fast suspend/resume

rk29: backlight: fix kernel BUG by double add_timer while fast suspend/resume

fix this bug:
kernel BUG at kernel/timer.c:791!
Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = c0404000
[00000000] *pgd=00000000
Internal error: Oops: 817 [#1] PREEMPT
last sysfs file: /sys/devices/platform/rk29_i2c.0/i2c-0/0-0055/power_supply/bq27510-battery/status
Modules linked in: wlan
CPU: 0    Not tainted  (2.6.32.27 #2)
PC is at __bug+0x18/0x24
LR is at __bug+0x14/0x24
[<c042b3c8>] (__bug+0x18/0x24) from [<c0453680>] (add_timer+0x1c/0x2c)
[<c0453680>] (add_timer+0x1c/0x2c) from [<c0476348>] (late_resume+0x104/0x158)
[<c0476348>] (late_resume+0x104/0x158) from [<c045a7bc>] (worker_thread+0x180/0x22c)
[<c045a7bc>] (worker_thread+0x180/0x22c) from [<c045dfac>] (kthread+0x78/0x80)
[<c045dfac>] (kthread+0x78/0x80) from [<c042899c>] (kernel_thread_exit+0x0/0x8)