staging: lustre: llite: remove redundant lookup in dump_pgcache

Both the 'next' and the 'show' functions for the dump_page_cache
seqfile perform a lookup based on the current file index.  This is
needless duplication.

The reason appears to be that the state that needs to be communicated
from "next" to "show" is two pointers, but seq_file only provides for
a single pointer to be returned from next and passed to show.

So make use of the new 'seq_private' structure to store the extra
pointer.
So when 'next' (or 'start') find something, it returns the page and
stores the clob in the private area.
'show' accepts the page as an argument, and finds the clob where it
was stored.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>