tests: Make ap_hs20_fetch_osu more robust under heavy load

Use scan_for_bss() instead of scan() to avoid errors if the active scan
fails, e.g., due to heavy load under parallel-vm.sh test run.

Signed-off-by: Jouni Malinen <j@w1.fi>

tests/hwsim/test_ap_hs20.py

@@ -1924,7 +1924,7 @@ def test_ap_hs20_fetch_osu(dev, apdev):
         except:
             pass
     try:
-        dev[1].scan(freq="2412")
+        dev[1].scan_for_bss(bssid, freq="2412")
         dev[0].request("SET osu_dir " + dir)
         dev[0].request("FETCH_OSU")
         if "OK" not in dev[1].request("HS20_ICON_REQUEST " + bssid + " w1fi_logo"):