mds: set mdr->in[n] in rdlock_path_xlock_dentry
mds: set mdr->in[n] in rdlock_path_xlock_dentry

This keeps things consistent with what we'd get with
path_traverse.  Namely, it means that if done_locking gets
set to true, then a future call to rdlock_path_pin_ref can
bail out and return mdr->in[n] and get a correct value.

This fixes

 touch mnt/a
 ls mnt
 touch mnt/.ceph

mds hang on the create request.

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph