staging/xgifb: Consolidate if branches with similar conditions

1) The same condition (pVBInfo->IF_DEF_LVDS == 0) was checked in the if
clause directly in front of this one.

2) The same condition pVBInfo->VBType & (VB_SIS301B | VB_SIS302B |
VB_SIS301LV | VB_SIS302LV | VB_XGI301C) was checked in the if
clause directly in front of this one.

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