make sure to catch the right error so it is displayed as an error on the ui not a 500 (#4945)

models/ssh_key.go

@@ -732,7 +732,7 @@ func AddDeployKey(repoID int64, name, content string, readOnly bool) (*DeployKey
 
 	key, err := addDeployKey(sess, pkey.ID, repoID, name, pkey.Fingerprint, accessMode)
 	if err != nil {
-		return nil, fmt.Errorf("addDeployKey: %v", err)
+		return nil, err
 	}
 
 	return key, sess.Commit()