staging: xgifb: delete redundant extended register access enable

The extended register access enable in !XGIvga_enabled case is not needed.
The driver has enabled the access unconditionally already earlier in
the routine.

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