libertas: don't use __lbs_cmd() with empty callback in if_usb.c

We're about to change semantics, leaving callers of
lbs_prepare_and_send_command() with the old broken priv->cur_cmd_retcode
crap. The existence of the callback command will be the trigger for the
new semantics when handling the response.
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/if_usb.c

@@ -109,7 +109,7 @@ static void if_usb_set_boot2_ver(struct lbs_private *priv)
 	b2_cmd.action = 0;
 	b2_cmd.version = priv->boot2_version;
 
-	if (lbs_cmd(priv, CMD_SET_BOOT2_VER, &b2_cmd, NULL, 0))
+	if (lbs_cmd_with_response(priv, CMD_SET_BOOT2_VER, &b2_cmd))
 		lbs_deb_usb("Setting boot2 version failed\n");
 }