nubus: 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: linux-m68k@lists.linux-m68k.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>