mt76: fix antenna config missing in 6G cap

To make sure we have the proper antenna config in 6g cap,
move IEEE80211_VHT_CAP_[T/R]X_ANTENNA_PATTERN to stream init.

Fixes: edf9dab8

 ("mt76: add 6GHz support")
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>