dracut-functions: fixed inst() for mkinitrd compat

dracut-functions

@@ -264,7 +264,11 @@ inst() {
         derror "inst only takes 1 or 2 or 3 arguments"
 	exit 1
     fi
-    [[ "$2" = "$initdir" ]] && set $1 $3
+    if [[ $# = 3 ]]; then
+	[[ -z $initdir ]] && initdir=$2; 
+        export initdir
+        set $1 $3
+    fi
     for x in inst_symlink inst_script inst_binary inst_simple; do
        $x "$@" && return 0
     done