libceph: put request only if it's done in handle_reply()

handle_reply() may be called twice on the same request: on ack and then
on commit.  This occurs on btrfs-formatted OSDs or if cephfs sync write
path is triggered - CEPH_OSD_FLAG_ACK | CEPH_OSD_FLAG_ONDISK.

handle_reply() handles this with the help of done_request().

Fixes: 5aea3dcd ("libceph: a major OSD client update")
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>