ceph: trigger the reclaim work once there has enough pending caps

The nr in ceph_reclaim_caps_nr() is very possibly larger than 1,
so we may miss it and the reclaim work couldn't triggered as expected.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>