ceph: wait on async create before checking caps for syncfs

Currently, we'll call ceph_check_caps, but if we're still waiting
on the reply, we'll end up spinning around on the same inode in
flush_dirty_session_caps. Wait for the async create reply before
flushing caps.

Cc: stable@vger.kernel.org
URL: https://tracker.ceph.com/issues/55823
Fixes: fbed7045

 ("ceph: wait for async create reply before sending any cap messages")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>