USB: gadget: udc: Process disconnect synchronously

As the comment in usb_disconnect() hints, do not defer the
disconnect processing, and instead just do it directly in
the irq handler. This allows the driver to avoid using a
nowadays deprecated tasklet.

Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lore.kernel.org/r/20210119001653.127975-1-dave@stgolabs.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>