wifi: mt76: connac: fix EHT phy mode check

wifi: mt76: connac: fix EHT phy mode check

[ Upstream commit 2c2f50bf6407e1fd43a1a257916aeaa5ffdacd6c ]

Add a BSS eht_support check before returning EHT phy mode. Without this
patch, there might be an inconsistency where the softmac layer thinks
the BSS is in HE mode, while the FW thinks it is in EHT mode.

Signed-off-by: MeiChia Chiu <meichia.chiu@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Sasha Levin <sashal@kernel.org>