scripts/arm-magic.sh: switch to /bin/sh

This does not use any special bash stuff.

Signed-off-by: Rosen Penev <[email protected]>

scripts/arm-magic.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 #
 #   Empty/wrong machtype-workaround generator
 #