staging/xgifb: Remove unused values in XG27_SR13 and XGI340_SR13

 In the lookup tables XG27_SR13 and XGI340_SR13 only the first three
 values are used of each 'line', thus the remaining fields can be
 removed.

Rationale:
- vb_init.c uses pVBInfo->ram_type for the 'column' index for
pVBInfo->SR15.

- pVBInfo->ram_type is assigned the return value of
XGINew_GetXG20DRAMType which can only be 0, 1 or 2

- pVBInfo->SR15 is assigned to either XG27_SR13 or XGI340_SR13 in
vb_setmode.c

-> only the first three values are used.
This becomes also evident as values 3-7 are all 0.

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