staging: xgifb: assume the default video mode also when module

The same default video mode should be assumed regardless if the driver
is a module or not. This won't change the current behaviour, but it will
simplify further changes.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>