release_pages() has been available to modules since Oct, 2010,
when commit 0be8557b ("fuse: use release_pages()") added
EXPORT_SYMBOL(release_pages). However, this ceph code was still
using a workaround.

Remove the workaround, and call release_pages() directly.
Signed-off-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NJeff Layton <jlayton@kernel.org>
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>