libceph: unregister request in __map_request failed and nofail == false

For nofail == false request, if __map_request failed, the caller does
cleanup work, like releasing the relative pages.  It doesn't make any sense
to retry this request.

CC: stable@vger.kernel.org
Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Reviewed-by: Sage Weil <sage@inktank.com>

net/ceph/osd_client.c

@@ -2129,6 +2129,8 @@ int ceph_osdc_start_request(struct ceph_osd_client *osdc,
 			dout("osdc_start_request failed map, "
 				" will retry %lld\n", req->r_tid);
 			rc = 0;
+		} else {
+			__unregister_request(osdc, req);
 		}
 		goto out_unlock;
 	}