hurd: Fix warnings

hurd: Fix warnings

	* hurd/hurd/lookup.h (__hurd_file_name_lookup, hurd_file_name_lookup,
	__hurd_file_name_split, hurd_file_name_split,
	__hurd_directory_name_split, hurd_directory_name_split,
	__hurd_file_name_lookup_retry, hurd_file_name_lookup_retry,
	hurd_file_name_path_lookup): Make lookup function parameter take a
	const char *name instead of char *name.
	* hurd/hurdlookup.c (__hurd_file_name_lookup, __hurd_file_name_split,
	__hurd_directory_name_split): Likewise.
	* hurd/lookup-retry.c (__hurd_file_name_lookup_retry): Likewise.
	* hurd/path-lookup.c (hurd_file_name_path_lookup): Likewise.