staging/xgifb: Remove unused variables and dead assignments

The variables A,HBS and VBS are never read in XGIfb_mode_rate_to_ddata
and the assignment has no side effects -> so we can simply remove them.
Removing them causes VT, HT and cr_data3 to be unused -> remove them as well
and remove the assignmens to cr_data which are shadowed by a different
assignment a few lines later.

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