drivers/gpu/drm/gma500/backlight.c: fix a defined-but-not-used warning for do_gma_backlight_set()

Fix the following warning:

	drivers/gpu/drm/gma500/backlight.c:29:13: warning: 'do_gma_backlight_set' defined but not used [-Wunused-function]

by moving the entire function inside the conditional section currently
inside of it.  All the places that call it are so conditionalised.

Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>