ds1620: Don't use create_proc_read_entry()

Don't use create_proc_read_entry() as that is deprecated, but rather use
proc_create_data() and seq_file instead.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Arnd Bergmann <arnd@arndb.de>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>