wifi: cfg80211: lock wiphy mutex for rfkill poll

[ Upstream commit 8e2f6f23 ]

We want to guarantee the mutex is held for pretty much
all operations, so ensure that here as well.

Reported-by:  <syzbot+7e59a5bfc7a897247e18@syzkaller.appspotmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>