staging: xgifb: vb_setmode: eliminate GetVGAType/Set_VGAType

Eliminate unneeded function and struct field. The same information is
available in HwDeviceExtension->jChipType.

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