btrfs: always use left leaf variable in __push_leaf_right()

The 'left' variable points to path->nodes[0] and path->nodes[0] is never
changed, but some places use 'left' while others refer to path->nodes[0].
Update all sites to use 'left' as not only it's shorter it's also easier
to reason since it means the left leaf and avoids any confusion with the
sibling right leaf.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/ctree.c

@@ -3240,10 +3240,10 @@ static noinline int __push_leaf_right(struct btrfs_trans_handle *trans,
 	/* then fixup the leaf pointer in the path */
 	if (path->slots[0] >= left_nritems) {
 		path->slots[0] -= left_nritems;
-		if (btrfs_header_nritems(path->nodes[0]) == 0)
-			btrfs_clear_buffer_dirty(trans, path->nodes[0]);
-		btrfs_tree_unlock(path->nodes[0]);
-		free_extent_buffer(path->nodes[0]);
+		if (btrfs_header_nritems(left) == 0)
+			btrfs_clear_buffer_dirty(trans, left);
+		btrfs_tree_unlock(left);
+		free_extent_buffer(left);
 		path->nodes[0] = right;
 		path->slots[1] += 1;
 	} else {