ceph: fix fscache invalidation

[ Upstream commit 10a7052c7868bc7bc72d947f5aac6f768928db87 ]

Ensure that we invalidate the fscache whenever we invalidate the
pagecache.

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