staging/xgifb: fix dumpVGAReg compile error if DEBUG is set

If DEBUG is set dumpVGAReg is called and tries to access
XGISR which is defined as (xgifb_info->dev_info.P3c4)
which is not known within this function.

-> add as parameter to dumpVGAReg so xgifb_info becomes known

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