usb/ohci: Set pad to 0 after frame update

When the OHCI controller's framenumber is incremented, HccaPad1 register
should be set to zero (Ref OHCI Spec 4.4)

ReactOS uses hccaPad1 to determine if the OHCI hardware is running,
consequently it fails this check in current qemu master.

Signed-off-by: Ryan Wendland <wendland@live.com.au>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1048


Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>