ceph: use pagevec_lookup_range_nr_tag()

Use new function for looking up pages since nr_pages argument from
pagevec_lookup_range_tag() is going away.

Link: http://lkml.kernel.org/r/20171009151359.31984-14-jack@suse.cz


Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>