wifi: cfg80211: fix RCU dereference in __cfg80211_bss_update

[ Upstream commit 1184950e ]

Replace rcu_dereference() with rcu_access_pointer() since we hold
the lock here (and aren't in an RCU critical section).

Fixes: 32af9a9e

 ("wifi: cfg80211: free beacon_ies when overridden from hidden BSS")
Reported-and-tested-by:  <syzbot+864a269c27ee06b58374@syzkaller.appspotmail.com>
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Link: https://msgid.link/tencent_BF8F0DF0258C8DBF124CDDE4DD8D992DCF07@qq.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>