Btrfs: fix double increment of path->slots[0] in btrfs_next_leaf

if 1 is returned by btrfs_search_slot, the path already points to the
first item with 'key > searching key'. So increasing path->slots[0] by
one is superfluous in that case.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.c

@@ -4146,6 +4146,7 @@ again:
 	 * advance the path if there are now more items available.
 	 */
 	if (nritems > 0 && path->slots[0] < nritems - 1) {
+		if (ret == 0)
 			path->slots[0]++;
 		ret = 0;
 		goto done;