mt76x2: fix tssi initialization for 5GHz band

Fix mcu initial configuration for tssi calibration on 5GHz band

Fixes: 7bc04215

 ("mt76: add driver code for MT76x2e")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Acked-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>