staging/xgifb: simplify vga I/O ports handling

XGIfb driver transfers integer port number through several typecasts via
pjIOAddress field. Drop that field completely and use vga_base field of
xgifb_info directly.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>