usb: gadget: core: force synchronous registration

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: fc274c1e99731 ("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.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>