staging/xgifb: remove unused variables

XGI_P3cc is unused and the assignment without side effects -> remove;
Data can be simply replaced by the Temp variable, which was changed to
temp in order to make checkpatch happy.

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