mt7601u: check chip version on probe

Since some USB device IDs are duplicated between mt7601u and mt76x0u
devices, check chip version on probe and return error if not match
0x7601.

Don't think this is serious issue, probe most likely will fail at
some other point for wrong device, but we do not have to configure
it if we know is not mt7601u device.

Reported-by: Xose Vazquez Perez <xose.vazquez@gmail.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Jakub Kicinski <kubakici@wp.pl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>