usb: add short-packet handling to usb-storage driver

usb: add short-packet handling to usb-storage driver

The dwc-hsotg (dwc2) USB host depends on a short packet to
indicate the end of an IN transfer. The usb-storage driver
currently doesn't provide this, so fix it.

I have tested this change rather extensively using a PC
emulation with xhci, ehci, and uhci controllers, and have
not observed any regressions.

Signed-off-by: Paul Zimmerman <pauldzim@gmail.com>
Message-id: 20200520235349.21215-6-pauldzim@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>