ceph: silence smatch warning in reconnect_caps_cb()

Smatch static checker warning:

  fs/ceph/mds_client.c:3968 reconnect_caps_cb()
  warn: missing error code here? '__get_cap_for_mds()' failed. 'err' = '0'

[ idryomov: Dan says that Smatch considers it intentional only if the
  "ret = 0;" assignment is within 4 or 5 lines of the goto. ]

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>