RDMA/hfi1: fix array termination by appending NULL to attr array

This fixes a kernel panic when loading the hfi driver as a dynamic module.

Signed-off-by: Steven L Roberts <robers97@gmail.com>
Reviewed-by: Leon Romanovsky <leon@kernel.org>
Acked-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>