hw/usb/hcd-dwc2: fix divide-by-zero in dwc2_handle_packet()

hw/usb/hcd-dwc2: fix divide-by-zero in dwc2_handle_packet()

Check the value of mps to avoid potential divide-by-zero later in the function.
Since HCCHAR_MPS is guest controllable, this prevents a malicious/buggy guest
from crashing the QEMU process on the host.

Signed-off-by: Mauro Matteo Cascella <mcascell@redhat.com>
Reviewed-by: Paul Zimmerman <pauldzim@gmail.com>
Reported-by: Gaoning Pan <gaoning.pgn@antgroup.com>
Reported-by: Xingwei Lin <linyi.lxw@antfin.com>
Message-id: 20201015075957.268823-1-mcascell@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>