ceph: Fix infinite loop in __wake_requests

ceph: Fix infinite loop in __wake_requests

__wake_requests() will enter infinite loop if we use it to wake
requests in the session->s_waiting list. __wake_requests() deletes
requests from the list and __do_request() adds requests back to
the list.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Sage Weil <sage@inktank.com>
(cherry picked from commit ed75ec2cd19b47efcd292b6e23f58e56f4c5bc34)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>