AK3: fix partition detection taking first match on older devices

- `test -e` could fail due to unexpanded *'s in $target

tools/ak3-core.sh

@@ -678,7 +678,9 @@ setup_ak() {
             else
               abort "Unable to determine mtd $block partition. Aborting...";
             fi;
-            target=/dev/mtd/$mtdname;
+            if [ -e /dev/mtd/$mtdname ]; then
+              target=/dev/mtd/$mtdname;
+            fi;
           elif [ -e /dev/block/by-name/$part ]; then
             target=/dev/block/by-name/$part;
           elif [ -e /dev/block/bootdevice/by-name/$part ]; then
@@ -690,7 +692,7 @@ setup_ak() {
           elif [ -e /dev/$part ]; then
             target=/dev/$part;
           fi;
-          test -e "$target" && break 2;
+          test "$target" && break 2;
         done;
       done;
       if [ "$target" ]; then