libceph: remove unnecessary ret variable in ceph_auth_init()

There is no necessary to define variable assignment, just return
directly to simplify the steps.

Signed-off-by: zuoqilin <zuoqilin@yulong.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>