staging: vt6656: rxtx.c: s_uGetDataDuration remove First Frag or Mid Frag dead code.

The driver always calls s_uGetDataDuration with;
uFragIdx = 0, cbLastFragmentSize = 0 and uMACfragNum = 1

uFragIdx == (uMACfragNum-1) is always true and bLastFrag = 1.

Remove dead First Frag or Mid Frag if/else and variables.

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