ceph: do not call __mark_dirty_inode under i_lock

The __mark_dirty_inode helper now takes i_lock as of 250df6ed

.  Fix the
one ceph callers that held i_lock (__ceph_mark_dirty_caps) to return the
flags value so that the callers can do it outside of i_lock.

Signed-off-by: Sage Weil <sage@newdream.net>