backlight: platform_lcd: fix checkpatch error

This patch fixes the checkpatch error as below:

  ERROR: spaces prohibited around that ':' (ctx:WxW)

Signed-off-by: Jingoo Han <jg1.han@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>