staging: vt6656: rxtx.c: s_uGetDataDuration remove dead variables.

As result of patch
staging: vt6656: rxtx.c s_uGetDataDuration remove First Frag or Mid Frag dead code.

cbFrameLength, wRate, uFragIdx, cbLastFragmentSize, uMACfragNum, byFBOption are
dead variables.

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