mt76x02: fixup MT_PROT_RATE_* defines

On new mt76 chips, phy mode is configured by last 3 bits
of rate value. Hence OFDM bit is marked by 0x2000
instead of 0x4000.

Acked-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>