usb: gadget: core: force synchronous registration

Registering a gadget driver is expected to complete synchronously and
immediately after calling driver_register() this function checks that
the driver has bound so as to return an error.

Set PROBE_FORCE_SYNCHRONOUS to ensure this is the case even when
asynchronous probing is set as the default.

Fixes: fc274c1e ("USB: gadget: Add a new bus for gadgets")
Cc: stable@vger.kernel.org
Signed-off-by: John Keeping <jkeeping@inmusicbrands.com>
Link: https://lore.kernel.org/r/20240913102325.2826261-1-jkeeping@inmusicbrands.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/core.c

@@ -1696,6 +1696,7 @@ int usb_gadget_register_driver_owner(struct usb_gadget_driver *driver,
 	driver->driver.bus = &gadget_bus_type;
 	driver->driver.owner = owner;
 	driver->driver.mod_name = mod_name;
+	driver->driver.probe_type = PROBE_FORCE_SYNCHRONOUS;
 	ret = driver_register(&driver->driver);
 	if (ret) {
 		pr_warn("%s: driver registration failed: %d\n",