staging/rdma/hfi1: actually use new RNR timer API in loopback path

The patch series which added a new API for the RNR timer did not include an
updated call in the loopback path. RC/UC RNR loopback would be broken
without this.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>