Bluetooth: bpa10x: Use h4_recv_buf helper for frame reassembly

The manually coded frame reassembly is actually broken. The h4_recv_buf
helper from the UART driver is a perfect fit for frame reassembly for
this driver. So just export that function and use it here as well.

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 6299954..c9c5dd0 100644
--- a/drivers/bluetooth/Kconfig
+++ b/drivers/bluetooth/Kconfig
@@ -184,6 +184,7 @@
 config BT_HCIBPA10X
 	tristate "HCI BPA10x USB driver"
 	depends on USB
+	select BT_HCIUART_H4
 	help
 	  Bluetooth HCI BPA10x USB driver.
 	  This driver provides support for the Digianswer BPA 100/105 Bluetooth