fb: handle allocation failure in alloc_apertures()

If the kzalloc() fails we should return NULL.  All the places that call
alloc_apertures() check for this already.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: James Simmons <jsimmons@infradead.org>
Acked-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/linux/fb.h

@@ -873,6 +873,8 @@ struct fb_info {
 static inline struct apertures_struct *alloc_apertures(unsigned int max_num) {
 	struct apertures_struct *a = kzalloc(sizeof(struct apertures_struct)
 			+ max_num * sizeof(struct aperture), GFP_KERNEL);
+	if (!a)
+		return NULL;
 	a->count = max_num;
 	return a;
 }