USB: serial: mxuport: add endpoint sanity check

Add an explicit sanity check to make sure we have the expected
endpoints. This will provide a descriptive error message in case an
expected endpoint is missing when probing.

Note that the driver already gracefully fails to probe (albeit with a
less descriptive error message) if a bulk-in endpoint is missing, and an
attempt to write to a port whose device lack a bulk-out endpoint would
fail with -ENODEV.
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/mxuport.c

@@ -1373,6 +1373,8 @@ static struct usb_serial_driver mxuport_device = {
 	},
 	.description		= "MOXA UPort",
 	.id_table		= mxuport_idtable,
+	.num_bulk_in		= 2,
+	.num_bulk_out		= 1,
 	.probe			= mxuport_probe,
 	.port_probe		= mxuport_port_probe,
 	.attach			= mxuport_attach,