ceph: drop pinned_page parameter from ceph_get_caps

All of the existing callers that don't set this to NULL just drop the
page reference at some arbitrary point later in processing. There's no
point in keeping a page reference that we don't use, so just drop the
reference immediately after checking the Uptodate flag.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>