wifi: mac80211: unlock on error in ieee80211_can_powered_addr_change()

Unlock before returning -EOPNOTSUPP.

Fixes: 3c06e91b ("wifi: mac80211: Support POWERED_ADDR_CHANGE feature")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>