dm ingerity: pass size to dm_integrity_alloc_page_list()

Pass size to dm_integrity_alloc_page_list().  This is needed so
following commits can pass a size that is different from
ic->journal_pages.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>