wifi: mac80211: adjust scan cancel comment/check

Instead of the comment about holding RTNL, which is now wrong,
add a proper lockdep assertion for the wiphy mutex.

Fixes: a05829a7 ("cfg80211: avoid holding the RTNL when calling the driver")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230301115906.84352e46f342.Id90fef8c581cebe19cb30274340cf43885d55c74@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>