mb/google/cyan/acpi: Replace Add(a,b,c) with ASL 2.0 syntax

Replace `Add (a, b, c)` with `c = a + b`.

Change-Id: I771c855e8885238c7fc3b0a7a6e9c2002274c0f2
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60490
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

@@ -206,7 +206,7 @@ Device (DPTF)
 		Multiply (Arg0, 10, Local0)
 
 		/* Convert to Kelvin */
-		Add (Local0, 2732, Local0)
+		Local0 += 2732
 
 		Return (Local0)
 	}