wifi: mt76: connac: use muar idx 0xe for non-mt799x as well

This is expected by the firmware of older chipsets as well, though it may
not have been as strongly required as on mt799x

Fixes: 098428c4 ("wifi: mt76: connac: set correct muar_idx for mt799x chipsets")
Signed-off-by: Felix Fietkau <nbd@nbd.name>