staging/xgifb: Remove unused variable and dead assignment

modeflag is unused in XGI_SetSeqRegs, XGI_GetTVInfo,
  XGI_SetLCDRegs, XGI_GetRatePtrCRT2 -> remove

resinfo is unused in XGI_PreSetGroup1, XGI_SetGroup1, XGI_SetGroup2,
  XGI_SetLCDRegs -> remove

push1,push2 are unused in XGI_SetLCDRegs -> remove

CRT1Index is unused in XGI_PreSetGroup1, XGI_SetLockRegs,
  XGI_SetLCDRegs -> remove

tempcx in XGI_PreSetGroup1 only holds the values 4,5,6
  -> change its type to u8

crt2crtc is unused in XGI_SetGroup2 -> remove

CRT2Index is unused in XGI_GetVCLK2Ptr -> remove.

Assignment to i is dead in XGI_SetSeqRegs since it is not used before
  the next assignment -> remove the dead assignment.

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