scripts/mkimg.standard.sh: use `case ... in`

scripts/mkimg.standard.sh

@@ -10,13 +10,16 @@ profile_standard() {
 	output_format="iso"
 	kernel_cmdline="nomodeset"
 	kernel_addons="xtables-addons"
-	if [ "$ARCH" = "s390x" ]; then
+	case "$ARCH" in
+	s390x)
 		apks="$apks s390-tools"
 		initfs_features="$initfs_features dasd_mod qeth"
 		initfs_cmdline="modules=loop,squashfs,dasd_mod,qeth quiet"
-	fi
-	if [ "$ARCH" = "ppc64le" ]; then
+		;;
+	ppc64le)
 		initfs_cmdline="modules=loop,squashfs,sd-mod,usb-storage,ibmvscsi quiet"
+		;;
+	esac
 	fi
 }