mb/google/kahlee/acpi: Replace Index() with ASL 2.0 syntax

Replace `Index (FOO, 0)` with `FOO[0]`.

Change-Id: I81a2d63db3e3575acd91ea99e1490701889b896f
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60560
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/mainboard/google/kahlee/variants/baseboard/include/baseboard/acpi/sleep.asl

@@ -30,8 +30,8 @@ Method (_PTS, 1)
 
 	/* Clear wake status structure. */
 	Store (0, PEWD)
-	Store (0, Index(WKST,0))
+	Store (0, WKST[0])
-	Store (0, Index(WKST,1))
+	Store (0, WKST[1])
 	Store (7, UPWS)
 }