UBI: get device when opening volume

When a volume is opened, get its kref via get_device() call.
And put the reference when closing the volume. With this, we
may have a bit saner volume delete.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/cdev.c b/drivers/mtd/ubi/cdev.c
index 24344ba..35d34b6 100644
--- a/drivers/mtd/ubi/cdev.c
+++ b/drivers/mtd/ubi/cdev.c
@@ -635,9 +635,12 @@
 		}
 
 		err = ubi_remove_volume(desc);
-		if (err)
-			ubi_close_volume(desc);
-
+		/*
+		 * The volume is deleted, and the 'struct ubi_volume' object
+		 * will be freed when 'ubi_close_volume()' will call
+		 * 'put_device()'.
+		 */
+		ubi_close_volume(desc);
 		break;
 	}