staging/xgifb: Remove dead assignments/increments

The code now contains several dead assignments which are shadowed by
another assignment a few lines later.

-> This patch removes them (and possibly associated code).

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>