staging/rdma/hfi1: Change for data type of port number

This commit changes the data type for port_num in
pma_get_opa_porterrors() from unsigned long to u8.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Sebastian Sanchez <sebastian.sanchez@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>