drivers/video/aty/aty128fb.c: fix a warning pertaining to the aty128fb backlight variable

Fix the following warning in the aty128fb driver:

	drivers/video/aty/aty128fb.c:363:12: warning: 'backlight' defined but not used [-Wunused-variable]
	 static int backlight = 0;
		    ^

as the variable's value is only read if CONFIG_FB_ATY128_BACKLIGHT=y.  The
variable is also set if MODULE is unset[*].

[*] I wonder if the conditional wrapper around aty128fb_setup() should be
    using CONFIG_MODULE rather than MODULE.

Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>