staging/xgifb: Don't write the same values x times

With the previous patch 'Move duplicated code for dram to helper
function' it becomes evident that the code is performing the same
thing 4 or 8 times in a row without changing arguments to the function
and thus writing the same values over and over again.

It was tested that these repeats are unnecessary.

-> we can safely remove them.

Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>