mt7601u: set device mac address in mt7601u_add_interface()

If mac80211 adds a vif with a different mac address respect to
the eeprom one, the device will not be able to connect to the ap
since the hw address has not been updated.
Fix the issue updating hw mac address in mt7601u_add_interface routine

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1516935


Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>