Improve message a bit.

Signed-off-by: Marko Saukko <marko.saukko@jollamobile.com>
Improve error message.

Signed-off-by: Marko Saukko <marko.saukko@jollamobile.com>
When there is no patches in VENDOR-master there is only 3 parameters
in _src. So lets not enforce 4 params.

Signed-off-by: Marko Saukko <marko.saukko@jollamobile.com>