Bluetooth: hci_uart: Use h4_recv_buf helper for Atheros AR300x

Instead of using hci_recv_stream_fragment, use the local available
h4_recv_buf helper function.

To ensure that the function is available select BT_HCIUART_H4.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
diff --git a/drivers/bluetooth/Kconfig b/drivers/bluetooth/Kconfig
index e8630b6..f8a4197 100644
--- a/drivers/bluetooth/Kconfig
+++ b/drivers/bluetooth/Kconfig
@@ -62,6 +62,7 @@
 config BT_HCIUART_ATH3K
 	bool "Atheros AR300x serial support"
 	depends on BT_HCIUART
+	select BT_HCIUART_H4
 	help
 	  HCIATH3K (HCI Atheros AR300x) is a serial protocol for
 	  communication between host and Atheros AR300x Bluetooth devices.