rk: backlight: unregister earlysuspend when shutdown

rk: backlight: unregister earlysuspend when shutdown

fix this warning:
WARNING: at drivers/gpio/gpiolib.c:101 gpio_ensure_requested+0x48/0x114()
autorequest GPIO-331
[<c043b170>] (unwind_backtrace+0x0/0xf0) from [<c0461800>] (warn_slowpath_common+0x4c/0x64)
[<c0461800>] (warn_slowpath_common+0x4c/0x64) from [<c0461898>] (warn_slowpath_fmt+0x2c/0x3c)
[<c0461898>] (warn_slowpath_fmt+0x2c/0x3c) from [<c05bb514>] (gpio_ensure_requested+0x48/0x114)
[<c05bb514>] (gpio_ensure_requested+0x48/0x114) from [<c05bbbb4>] (gpio_direction_output+0x7c/0xfc)
[<c05bbbb4>] (gpio_direction_output+0x7c/0xfc) from [<c044ccf8>] (rk29_backlight_pwm_suspend+0x54/0x74)
[<c044ccf8>] (rk29_backlight_pwm_suspend+0x54/0x74) from [<c05c3d0c>] (rk29_bl_suspend+0x78/0x90)
[<c05c3d0c>] (rk29_bl_suspend+0x78/0x90) from [<c0494374>] (early_suspend+0xc4/0x12c)
[<c0494374>] (early_suspend+0xc4/0x12c) from [<c04745c4>] (process_one_work+0x250/0x3ac)
[<c04745c4>] (process_one_work+0x250/0x3ac) from [<c0474b08>] (worker_thread+0x22c/0x3ec)
[<c0474b08>] (worker_thread+0x22c/0x3ec) from [<c047a484>] (kthread+0x80/0x88)
[<c047a484>] (kthread+0x80/0x88) from [<c04365f8>] (kernel_thread_exit+0x0/0x8)