IB/hfi1: Rename hdr2sc to hfi1_9B_get_sc5

IB/hfi1: Rename hdr2sc to hfi1_9B_get_sc5

The function really returned the 5-bit sc value from
the header and rhf. hdr2sc didn't quite describe what it did.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: Don Hiatt <don.hiatt@intel.com>
Signed-off-by: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>