drivers/video/backlight/s6e63m0.c: unregister backlight device and remove sysfs attribute file in s6e63m0_remove

s6e63m0_probe() registered backlight device and create sysfs attribute
files, thus s6e63m0_remove() should unregister backlight device and remove
sysfs attribute files.
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Richard Purdie <rpurdie@linux.intel.com>
Cc: InKi Dae <inki.dae@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>