Bluetooth: btmtkuart: fix recv_buf() return value

Serdev recv_buf() callback is supposed to return the amount of bytes
consumed, therefore an int in between 0 and count.

Do not return negative number in case of issue, just print an error and
return count. This fixes a WARN in ttyport_receive_buf().

Link: https://lore.kernel.org/all/087be419-ec6b-47ad-851a-5e1e3ea5cfcc@kernel.org/
Fixes: 7237c4c9 ("Bluetooth: mediatek: Add protocol support for MediaTek serial devices")
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

drivers/bluetooth/btmtkuart.c

@@ -336,7 +336,7 @@ mtk_stp_split(struct btmtkuart_dev *bdev, const unsigned char *data, int count,
 	return data;
 }
 
-static int btmtkuart_recv(struct hci_dev *hdev, const u8 *data, size_t count)
+static void btmtkuart_recv(struct hci_dev *hdev, const u8 *data, size_t count)
 {
 	struct btmtkuart_dev *bdev = hci_get_drvdata(hdev);
 	const unsigned char *p_left = data, *p_h4;
@@ -375,25 +375,20 @@ static int btmtkuart_recv(struct hci_dev *hdev, const u8 *data, size_t count)
 			bt_dev_err(bdev->hdev,
 				   "Frame reassembly failed (%d)", err);
 			bdev->rx_skb = NULL;
-			return err;
+			return;
 		}
 
 		sz_left -= sz_h4;
 		p_left += sz_h4;
 	}
-
-	return 0;
 }
 
 static int btmtkuart_receive_buf(struct serdev_device *serdev, const u8 *data,
 				 size_t count)
 {
 	struct btmtkuart_dev *bdev = serdev_device_get_drvdata(serdev);
-	int err;
 
-	err = btmtkuart_recv(bdev->hdev, data, count);
-	if (err < 0)
-		return err;
+	btmtkuart_recv(bdev->hdev, data, count);
 
 	bdev->hdev->stat.byte_rx += count;