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/decl.h b/drivers/net/wireless/libertas/decl.h
index f0de2a1..989fb77 100644
--- a/drivers/net/wireless/libertas/decl.h
+++ b/drivers/net/wireless/libertas/decl.h
@@ -17,7 +17,7 @@
 struct cmd_ctrl_node;
 struct cmd_ds_command;
 
-int lbs_set_mac_control(struct lbs_private *priv);
+void lbs_set_mac_control(struct lbs_private *priv);
 
 void lbs_send_tx_feedback(struct lbs_private *priv);