mac80211: allow driver to return error from sched_scan_stop

In order to solve races with sched_scan_stop, it is necessary
for the driver to be able to return an error to propagate that
to cfg80211 so it doesn't send an event.

Reviewed-by: Alexander Bondar <alexander.bondar@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index b211e41..836f500 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -1056,7 +1056,7 @@
 	local->sched_scan_req = NULL;
 
 	if (rcu_access_pointer(local->sched_scan_sdata))
-		drv_sched_scan_stop(local, sdata);
+		ret = drv_sched_scan_stop(local, sdata);
 
 out:
 	mutex_unlock(&local->mtx);