staging: xgifb: XGI_GetVBType(): delete IF_DEF_LVDS check

XGI_GetVBType() is called only for chips < XG20 so IF_DEF_LVDS cannot
be set.

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