mac80211: silence an uninitialized variable warning

We normally return an uninitialized value, but no one checks it so it
doesn't matter.  Anyway, let's silence the static checker warning.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

net/mac80211/tdls.c

@@ -1747,6 +1747,7 @@ ieee80211_process_tdls_channel_switch_resp(struct ieee80211_sub_if_data *sdata,
 		goto out;
 	}
 
+	ret = 0;
 call_drv:
 	drv_tdls_recv_channel_switch(sdata->local, sdata, &params);