Revert "discover_cached_paths() should not modify string from nvlist"

This reverts commit 8f14d92.

lib/libzutil/zutil_import.c

@@ -1565,21 +1565,12 @@ discover_cached_paths(libpc_handle_t *hdl, nvlist_t *nv,
 	 * our directory cache.
 	 */
 	if (nvlist_lookup_string(nv, ZPOOL_CONFIG_PATH, &path) == 0) {
-		int ret;
-		char *dir;
-		boolean_t freestr = B_FALSE;
-		if ((dl = zfs_dirnamelen(path)) == -1) {
-			dir = (char *)".";
-		} else {
-			if (asprintf(&dir, "%.*s", (int)dl, path) == -1)
-				return (ENOMEM);
-			freestr = B_TRUE;
-		}
-		ret = zpool_find_import_scan_dir(hdl, lock, cache,
-		    path, 0);
-		if (freestr)
-			free(dir);
-		return (ret);
+		if ((dl = zfs_dirnamelen(path)) == -1)
+			path = (char *)".";
+		else
+			path[dl] = '\0';
+		return (zpool_find_import_scan_dir(hdl, lock, cache,
+		    path, 0));
 	}
 	return (0);
 }