ceph: use errseq_t for writeback error reporting

Ensure that when writeback errors are marked that we report those to all
file descriptions that were open at the time of the error.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>