mt76x0: phy: fix bank check in mt76x0_rf_csr_{wr,rr}

Fix typo in bank check in mt76x0_rf_csr_{wr,rr} routines.
This issue has never been hit since mt76x0_rf_csr_{wr,rr}
are actually used just by pci code

Fixes: 10de7a8b

 ("mt76x0: phy files")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>