ec/google/chromeec/acpi: Replace Decrement() with ASL 2.0 syntax

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

Change-Id: Ie2d5856316e2c8faac657c6caf79a46f099353be
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60590
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/ec/google/chromeec/acpi/battery.asl

@@ -22,7 +22,7 @@ Method (BTSW, 1)
 	While (LNotEqual (BTIX, Arg0))
 	{
 		Sleep (1)
-		Decrement (Local0)
+		Local0--
 		If (LEqual (Local0, Zero))
 		{
 			Return (One)