libertas: cleanup a variable name

"&card->priv->driver_lock" and "&priv->driver_lock" are the same and
it's nicer to use the shorter one consistently.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/marvell/libertas/if_sdio.c

@@ -228,7 +228,7 @@ static int if_sdio_handle_cmd(struct if_sdio_card *card,
 	memcpy(priv->resp_buf[i], buffer, size);
 	lbs_notify_command_response(priv, i);
 
-	spin_unlock_irqrestore(&card->priv->driver_lock, flags);
+	spin_unlock_irqrestore(&priv->driver_lock, flags);
 
 	ret = 0;