ceph: fix getattr on directory when using norbytes

The norbytes mount option was broken, and when doing getattr
on a directory it return the rbytes instead of the number of
entities. This commit fixes it.

Signed-off-by: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>