UBI: fix compile warning

cdev.c whines in current git:

drivers/mtd/ubi/cdev.c: In function `major_to_device':
drivers/mtd/ubi/cdev.c:67: warning: control reaches end of non-void function

Shut it up.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/cdev.c b/drivers/mtd/ubi/cdev.c
index fb238d7..fe4da1e 100644
--- a/drivers/mtd/ubi/cdev.c
+++ b/drivers/mtd/ubi/cdev.c
@@ -64,6 +64,7 @@
 		if (ubi_devices[i] && ubi_devices[i]->major == major)
 			return ubi_devices[i];
 	BUG();
+	return NULL;
 }
 
 /**