Staging: xgifb: revert a warning fix and resolve it properly

Jiri pointed out that the previous compiler warning fix was incorrect as
the compiler was properly saying that the variable was not being set.
This was due to a #define commenting out all of the logic in the
function.

This patch reverts Javier's previous one, and properly fixes the issue
by making the function actually doing something.

Reported-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Javier Martinez Canillas <martinez.javier@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>