[virtwl] Fix host vfd_id base.

The virtio_wl device defines:

        VFD_ILLEGAL_SIGN_BIT: 0x80000000
        VFD_HOST_VFD_ID_BIT:  0x40000000

Test: Transmitting wl_keyboard keymap into sommelier.
Change-Id: Ia31537bc9bbffc601971e19da8c78d4ccdd5cc8a
2 files changed