staging: vt6656: csBeacon_xmit merge structures.

Merge structures typedef struct tagSTxShortBufHead and the members of
struct vnt_tx_datahead_ab to form single structure vnt_tx_short_buf_head.

Remove the duplicate members in struct vnt_beacon_buffer already in
typedef struct tagSTxShortBufHead.

This removes the need for any pointer arithmetic.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>