IB/hfi1: Correct 8051 link parameter settings

Two 8051 link settings, external device config and tuning method,
were written in the wrong location and the previous settings were
not cleared.  For both, clear the old value and write the new
value.

Fixes: 8ebd4cf1

 ("staging/rdma/hfi1: Add active and optical cable support")
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>