ec/hp/kbc1126/acpi: Use ASL 2.0 syntax to access arrays

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

Change-Id: Ie499f27acd13569095749e095d7898890da6985d
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60458
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/ec/hp/kbc1126/acpi/battery.asl

@@ -230,7 +230,7 @@ Method (\ISTR, 2, Serialized)
 	{
 		Local1--
 		Divide (Local0, 10, Local2, Local0)
-		Add (Local2, 48, Index (NUMB, Local1))
+		Add (Local2, 48, NUMB[Local1])
 	}
 	ToString (NUMB, Arg1, Local3)
 	Return (Local3)