mb/google/cyan/acpi: Use ASL 2.0 syntax to access arrays

Replace Index(FOO, 1337) with FOO[1337].

Change-Id: Ica59483c9e9f67361d269259708998f9152406f3
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60461
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/mainboard/google/cyan/variants/terra/include/variant/acpi/dptf.asl

@@ -173,7 +173,7 @@ Device (DPTF)
 	Method (_OSC, 4, Serialized)
 	{
 		/* Check for Passive Policy UUID */
-		If (LEqual (DeRefOf (Index (IDSP, 0)), Arg0)) {
+		If (LEqual (DeRefOf (IDSP[0]), Arg0)) {
 			/* Initialize Thermal Devices */
 			^TINI ()