ceph: clean up and optimize ceph_check_delayed_caps()

Make this loop look a bit more sane. Also optimize away the spinlock
release/reacquire if we can't get an inode reference.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>