xhci: drop XHCITransfer->{slotid,epid}

We can use XHCITransfer->epctx->{slotid,epid} instead.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1474965172-30321-8-git-send-email-kraxel@redhat.com