wl1271: set null data template when BSSID is known

The call to wl1271_cmd_build_null_data() was missing when we got associated,
this was causing PS to fail.  This patch adds the call and now PS seems to
work.
Signed-off-by: NLuciano Coelho <luciano.coelho@nokia.com>
Reviewed-by: NJuuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/wl12xx/wl1271_main.c

@@ -1545,6 +1545,12 @@ static void wl1271_op_bss_info_changed(struct ieee80211_hw *hw,
 	    memcmp(wl->bssid, bss_conf->bssid, ETH_ALEN)) {
 			wl->rx_config |= CFG_BSSID_FILTER_EN;
 			memcpy(wl->bssid, bss_conf->bssid, ETH_ALEN);
+			ret = wl1271_cmd_build_null_data(wl);
+			if (ret < 0) {
+				wl1271_warning("cmd buld null data failed %d",
+					       ret);
+				goto out_sleep;
+			}
 			ret = wl1271_cmd_join(wl);
 			if (ret < 0) {
 				wl1271_warning("cmd join failed %d", ret);