usb: gadget: move bind() callback back to struct usb_composite_driver

This partly reverts 07a18bd7 ("usb gadget: don't save bind callback in
struct usb_composite_driver") and fixes new drivers. The section missmatch
problems was solved by whitelisting structs in question via __ref.

Cc: devel@driverdev.osuosl.org
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/multi.c b/drivers/usb/gadget/multi.c
index 7e5852a..13db7cc 100644
--- a/drivers/usb/gadget/multi.c
+++ b/drivers/usb/gadget/multi.c
@@ -343,6 +343,7 @@
 	.dev		= &device_desc,
 	.strings	= dev_strings,
 	.max_speed	= USB_SPEED_HIGH,
+	.bind		= multi_bind,
 	.unbind		= __exit_p(multi_unbind),
 	.iProduct	= DRIVER_DESC,
 	.needs_serial	= 1,
@@ -351,7 +352,7 @@
 
 static int __init multi_init(void)
 {
-	return usb_composite_probe(&multi_driver, multi_bind);
+	return usb_composite_probe(&multi_driver);
 }
 module_init(multi_init);