soc/intel/baytrail/acpi: Replace Index(a, b) with ASL 2.0 syntax

Change-Id: Iab611cda1083da4378a6e509d11ea26bdbb45edd
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/71503
Reviewed-by: Felix Singer <felixsinger@posteo.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/soc/intel/baytrail/acpi/dptf/charger.asl b/src/soc/intel/baytrail/acpi/dptf/charger.asl
index f8eac66..1b0bd78 100644
--- a/src/soc/intel/baytrail/acpi/dptf/charger.asl
+++ b/src/soc/intel/baytrail/acpi/dptf/charger.asl
@@ -45,8 +45,7 @@
 	Method (SPPC, 1)
 	{
 		/* Retrieve Control (index 4) for specified PPSS level */
-		Local0 = DeRefOf (Index (DeRefOf (Index
-			(\_SB.CHPS, ToInteger (Arg0))), 4))
+		Local0 = DerefOf (DerefOf (\_SB.CHPS[ToInteger (Arg0)])[4])
 
 		/* Pass Control value to EC to limit charging */
 		\_SB.PCI0.LPCB.EC0.CHGS (Local0)