btrfs: free path at an earlier point in btrfs_get_extent

trace_btrfs_get_extent() has nothing to do with path, place
btrfs_free_path ahead so that we can unlock path on error.

Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -6979,10 +6979,10 @@ insert:
 	err = btrfs_add_extent_mapping(fs_info, em_tree, &em, start, len);
 	write_unlock(&em_tree->lock);
 out:
+	btrfs_free_path(path);
 
 	trace_btrfs_get_extent(root, inode, em);
 
-	btrfs_free_path(path);
 	if (err) {
 		free_extent_map(em);
 		return ERR_PTR(err);