staging: vt6656: rxtx s_vFillRTSHead create union of vnt_rts*/vnt_cts* structures.

Only one of vnt_rts*/vnt_cts* structures are accessed at any one time.

Join these structures in to a single union.

These will eventually form the tail structure of vnt_tx_buffer and
include structures vnt_tx_datahead*

Structures in s_vFillCTSHead will join in next patch series.

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