Remove hw_atomic_mutex mutex in mt76x0_dev data structure
since mt76x0_phy_set_channel is already protected by mt76_dev
mutex while mt76x0_chip_onoff is used just at device probe or
cleanup
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com> Signed-off-by: Felix Fietkau <nbd@nbd.name>