backlight: rename corgibl_limit_intensity() to genericbl_limit_intensity()

The rename of corgibl_limit_intensity is missed in commit d00ba726


("backlight: Rename the corgi backlight driver to generic").  Let's fix it
now.

Signed-off-by: Axel Lin <axel.lin@gmail.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>