libertas: fix scheduling while atomic bug in CMD_MAC_CONTROL

The old code incorrectly used lbs_cmd_with_response() and now uses
lbs_cmd_async().

While there I noticed that there is no real useful return values for
asynchronous command functions, so I made the function "void".

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/libertas/assoc.c b/drivers/net/wireless/libertas/assoc.c
index 54161f1..fcea2a1 100644
--- a/drivers/net/wireless/libertas/assoc.c
+++ b/drivers/net/wireless/libertas/assoc.c
@@ -272,9 +272,7 @@
 	else
 		priv->mac_control &= ~CMD_ACT_MAC_WEP_ENABLE;
 
-	ret = lbs_set_mac_control(priv);
-	if (ret)
-		goto out;
+	lbs_set_mac_control(priv);
 
 	mutex_lock(&priv->lock);
 
@@ -304,9 +302,7 @@
 	memcpy(&priv->secinfo, &assoc_req->secinfo,
 		sizeof(struct lbs_802_11_security));
 
-	ret = lbs_set_mac_control(priv);
-	if (ret)
-		goto out;
+	lbs_set_mac_control(priv);
 
 	/* If RSN is already enabled, don't try to enable it again, since
 	 * ENABLE_RSN resets internal state machines and will clobber the