usb: Enforce iso endpoints never returing USB_RET_ASYNC

ehci was already testing for this, and we depend in various places
on no devices doing this, so lets move the check for this to the
usb core.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
