rtl8723au_bt: Fix to build on all kernels

The API changed at kernel 3.13.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>

rtk_btusb.c

@@ -30,6 +30,8 @@
 #include <linux/errno.h>
 #include <linux/skbuff.h>
 #include <linux/usb.h>
+#include <linux/version.h>
+
 #include <net/bluetooth/bluetooth.h>
 #include <net/bluetooth/hci_core.h>
 
@@ -606,9 +608,14 @@ static int btusb_flush(struct hci_dev *hdev)
 	return 0;
 }
 
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3, 13, 0))
+static int btusb_send_frame(struct hci_dev *hdev, struct sk_buff *skb)
+{
+#else
 static int btusb_send_frame(struct sk_buff *skb)
 {
-	struct hci_dev *hdev = (struct hci_dev *) skb->dev;
+	struct hci_dev *hdev = (struct hci_dev *)skb->dev;
+#endif
 	struct btusb_data *data = GET_DRV_DATA(hdev);
 	struct usb_ctrlrequest *dr;
 	struct urb *urb;