wifi: mt76: mt7915: fix list corruption after hardware restart

Since stations are recreated from scratch, all lists that wcids are added
to must be cleared before calling ieee80211_restart_hw.
Set wcid->sta = 0 for each wcid entry in order to ensure that they are
not added again before they are ready.

Fixes: 8a55712d ("wifi: mt76: mt7915: enable full system reset support")
Link: https://patch.msgid.link/20250827085352.51636-4-nbd@nbd.name


Signed-off-by: Felix Fietkau <nbd@nbd.name>