ceph: assign the ci only when the inode isn't NULL

The ceph_find_inode() may will fail and return NULL.

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