A short packet indicates the end of a transfer and marks the request as
complete.

Fixes: b84a8dee ("usb: gadget: add Faraday fotg210_udc driver")
Signed-off-by: Fabian Vogt <fabian@ritter-vogt.de>
Link: https://lore.kernel.org/r/20210324141115.9384-8-fabian@ritter-vogt.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>