greybus: es2: fix error return code in ap_probe()

Fix to return a negative error code from the es2_arpc_in_enable() error
handling case instead of 0, as done elsewhere in this function.

Fixes: 9d9d3777 ("greybus: es2: Add a new bulk in endpoint for APBridgeA RPC")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/greybus/es2.c

@@ -1548,7 +1548,8 @@ static int ap_probe(struct usb_interface *interface,
 	INIT_LIST_HEAD(&es2->arpcs);
 	spin_lock_init(&es2->arpc_lock);
 
-	if (es2_arpc_in_enable(es2))
+	retval = es2_arpc_in_enable(es2);
+	if (retval)
 		goto error;
 
 	retval = gb_hd_add(hd);