wifi: mt76: mt7996: fix locking in mt7996_mac_sta_rc_work()

The 'continue' statements need to be under spinlock, since
the spinlock needs to be held as a loop invariant.

Fixes: 0762bdd3 ("wifi: mt76: mt7996: rework mt7996_mac_sta_rc_work to support MLO")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>