soc/intel/common/opregion: Use enum cb_err as return value

Return CB_SUCCESS and CB_ERR instead of some integer.
Preparation to merge intel/soc and intel/nb opregion implementations.

Change-Id: Ib99fcfe347b98736979fc82ab3de48bfc6fc7dcd
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/20220
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/intel/apollolake/graphics.c

@@ -44,7 +44,7 @@ static unsigned long igd_write_opregion(device_t dev, unsigned long current,
 	printk(BIOS_DEBUG, "ACPI:    * IGD OpRegion\n");
 	opregion = (igd_opregion_t *)current;
 
-	if (!init_igd_opregion(opregion))
+	if (init_igd_opregion(opregion) != CB_SUCCESS)
 		return current;
 
 	current += sizeof(igd_opregion_t);