virtio-gpu: do not byteswap padding

virtio-gpu: do not byteswap padding

In Linux 5.16, the padding of struct virtio_gpu_ctrl_hdr has become a
single-byte field followed by a uint8_t[3] array of padding bytes,
and virtio_gpu_ctrl_hdr_bswap does not compile anymore.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211111110604.207376-2-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>