mb/aopen/dxplplusu/acpi: Replace Decrement() with ASL 2.0 syntax

Replace `Decrement (a)` with `a--`.

Change-Id: I4320d86ce91e7070dc10fcefff6cbc0956be9788
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60586
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/aopen/dxplplusu/acpi/e7505_pri.asl b/src/mainboard/aopen/dxplplusu/acpi/e7505_pri.asl
index d258ec9..f8c7b2e 100644
--- a/src/mainboard/aopen/dxplplusu/acpi/e7505_pri.asl
+++ b/src/mainboard/aopen/dxplplusu/acpi/e7505_pri.asl
@@ -49,7 +49,7 @@
 		CreateDWordField (MSBF, \_SB.MBRS._Y1D._LEN, MEM2)
 		And (\_SB.PCI0.TOLM, 0xF800, Local1)
 		ShiftRight (Local1, 0x04, Local1)
-		Decrement (Local1)
+		Local1--
 		If (LGreater (Local1, 0x10))
 		{
 			Local1 -= 0x0F