UBI: simplify internal interfaces

Instead of passing vol_id to all functions and then find
struct ubi_volume, pass struct ubi_volume pointer.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index a8cdbd0..3a88cf1 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -423,8 +423,9 @@
 void ubi_free_volume(struct ubi_device *ubi, struct ubi_volume *vol);
 
 /* upd.c */
-int ubi_start_update(struct ubi_device *ubi, int vol_id, long long bytes);
-int ubi_more_update_data(struct ubi_device *ubi, int vol_id,
+int ubi_start_update(struct ubi_device *ubi, struct ubi_volume *vol,
+		     long long bytes);
+int ubi_more_update_data(struct ubi_device *ubi, struct ubi_volume *vol,
 			 const void __user *buf, int count);
 
 /* misc.c */