staging/xgifb: Consolidate function almost identical calls in XGINew_GetXG21Sense

Instead of calling xgifb_reg_and_or with almost identical parameters in
a simple if/else scenario, we assign the changing parameter to a temp
variable and call xgifb_reg_and_or only from one location.

-> Easier to read, easier to understand (especially wrt the line breaks)

(For the if condition we don't need the Temp variable, so we can use the
value directly).

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