iwmc3200wifi: clarify potentially undefined operation in iwm_scan_ssids

  CC [M]  drivers/net/wireless/iwmc3200wifi/commands.o
drivers/net/wireless/iwmc3200wifi/commands.c: In function ‘iwm_scan_ssids’:
drivers/net/wireless/iwmc3200wifi/commands.c:911:15: warning: operation on ‘iwm->scan_id’ may be undefined
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwmc3200wifi/commands.c

@@ -908,7 +908,7 @@ int iwm_scan_ssids(struct iwm_priv *iwm, struct cfg80211_ssid *ssids,
 		return ret;
 	}
 
-	iwm->scan_id = iwm->scan_id++ % IWM_SCAN_ID_MAX;
+	iwm->scan_id = (iwm->scan_id + 1) % IWM_SCAN_ID_MAX;
 
 	return 0;
 }