drivers/video/backlight/ld9040.c: small fixes

- Fix checking of wrong return value for backlight_device_register()

- Properly free allocated resources in ld9040_probe() error path and
  ld9040_remove().

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Donghwa Lee <dh09.lee@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>