soc/intel/apollolake/acpi: Replace Subtract(a,b,c) with ASL 2.0 syntax

Replace `Subtract (a, b, c)` with `c = a - b`.

Change-Id: I8c98f4e3c3aed6209fd36398134a36778a560708
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60481
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/soc/intel/apollolake/acpi/northbridge.asl

@@ -109,7 +109,7 @@ Method (_CRS, 0, Serialized)
 		/* Set 64bit MMIO resource base and length */
 		Store (A4GS, MLEN)
 		Store (A4GB, MMIN)
-		Subtract (Add (MMIN, MLEN), 1, MMAX)
+		MMAX = Add (MMIN, MLEN) - 1
 	}
 
 	Return (MCRS)