mt76: mt7921: use correct iftype data on 6GHz cap init

Set 6GHz cap to iftype data which is matched to the type of
current interface.

Fixes: 50ac15a5

 ("mt76: mt7921: add 6GHz support")
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>