video/backlight: remove obsolete cleanup for clientdata

A few new i2c-drivers came into the kernel which clear the
clientdata-pointer on exit or error.  This is obsolete meanwhile, the core
will do it.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Paul Mundt <lethal@linux-sh.org>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>