staging/xgifb: Fix always false condition in vb_setmode.c (smatch)

Smatch complains:
drivers/staging/xgifb/vb_setmode.c:3181
XGI_SetLockRegs() warn: bitwise AND condition is false here

Since SetNTSCTV is defined as 0 in drivers/video/sis/initdef.h this is
correct.
-> Change the condition to == to fix this.

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