libertas: don't spin_unlock_irq() twice

priv->driver_lock has already been unlocked some lines above. This patch
fixes the sparse warning:

drivers/net/wireless/libertas/main.c:792:6: warning: context problem in 'lbs_thread': '_spin_unlock_irq' expected different context
drivers/net/wireless/libertas/main.c:792:6:    context 'lock': wanted >= 1, got 0
Signed-of-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/main.c

@@ -788,11 +788,8 @@ static int lbs_thread(void *data)
 					le16_to_cpu(cmdnode->cmdbuf->command));
 				lbs_complete_command(priv, cmdnode, -ETIMEDOUT);
 				priv->nr_retries = 0;
-				if (priv->reset_card) {
-					spin_unlock_irq(&priv->driver_lock);
+				if (priv->reset_card)
 					priv->reset_card(priv);
-					spin_lock_irq(&priv->driver_lock);
-				}
 			} else {
 				priv->cur_cmd = NULL;
 				lbs_pr_info("requeueing command 0x%04x due "