mt76: mt7915: report rx mode value in mt7915_mac_fill_rx_rate

Report rx mode in mt7915_mac_fill_rx_rate routine in order to properly
add he radiotap if mode is at least HE_SU.

Fixes: 1c9db0aa ("mt76: mt7915: update rx rate reporting for mt7916")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>