usb: dwc3: gadget: fix high speed multiplier setting

For High-Speed Transfers the prepare_one_trb function is calculating the
multiplier setting for the trb based on the length parameter of the trb
currently prepared. This assumption is wrong. For trbs with a sg list,
the length of the actual request has to be taken instead.

Fixes: 40d829fb

 ("usb: dwc3: gadget: Correct ISOC DATA PIDs for short packets")
Cc: stable <stable@kernel.org>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20220704141812.1532306-3-m.grzeschik@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>