bcachefs: acl: Add missing check in bch2_acl_chmod()

The "ret = bkey_err(k);" assignment was accidentally left out so the
call to bch2_btree_iter_peek_slot() is not checked for errors.

Fixes: 53306e096d91 ("bcachefs: Always check for transaction restarts")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/acl.c

@@ -427,9 +427,10 @@ int bch2_acl_chmod(struct btree_trans *trans, subvol_inum inum,
 		return bch2_err_matches(ret, ENOENT) ? 0 : ret;
 
 	k = bch2_btree_iter_peek_slot(&iter);
-	xattr = bkey_s_c_to_xattr(k);
+	ret = bkey_err(k);
 	if (ret)
 		goto err;
+	xattr = bkey_s_c_to_xattr(k);
 
 	acl = bch2_acl_from_disk(trans, xattr_val(xattr.v),
 			le16_to_cpu(xattr.v->x_val_len));