9P: fix return value in v9fs_fid_xattr_set

v9fs_fid_xattr_set is supposed to return 0 on success.

This corrects the behaviour introduced in commit
bdd5c28d
"9p: fix return value in case in v9fs_fid_xattr_set()"

(The function returns a negative error on error, as expected)
Signed-off-by: NDominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: NEric Van Hensbergen <ericvh@gmail.com>

fs/9p/xattr.c

@@ -156,7 +156,7 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name,
 		offset += write_count;
 		value_len -= write_count;
 	}
-	retval = offset;
+	retval = 0;
 err:
 	p9_client_clunk(fid);
 	return retval;