nb/intel/snb: Don't run VGA oprom when libgfxinit is enabled

This was likely an oversight when libgfxinit got its own Kconfig
symbols.

Change-Id: I647551719b332b5b734720ae4ee0619bbfcbed8c
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33126
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/northbridge/intel/sandybridge/gma.c

@@ -626,7 +626,7 @@ static void gma_func0_init(struct device *dev)
 	/* Init graphics power management */
 	gma_pm_init_pre_vbios(dev);
 
-	if (!CONFIG(MAINBOARD_DO_NATIVE_VGA_INIT))
+	if (!CONFIG(MAINBOARD_USE_LIBGFXINIT))
 		/* PCI Init, will run VBIOS */
 		pci_dev_init(dev);