backlight: generic_bl: fix checkpatch warning

This patch fixes the checkpatch warning as below:

  WARNING: space prohibited between function name and open parenthesis '('

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>