ec/quanta/it8518/acpi: Replace Decrement() with ASL 2.0 syntax

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

Change-Id: Ibf5bdb1b3c2524194089b27a8af61b84f517e117
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60592
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/ec/quanta/it8518/acpi/battery.asl

@@ -67,7 +67,7 @@ Device (BATX)
 		{
 			// EC Is not ready
 			Sleep (5)
-			Decrement (Local0)
+			Local0--
 			If (LEqual (Local0, Zero))
 			{
 				Break