IB/hfi1: Correct issues with sc5 computation

There are several computatations of the sc in the
ud receive routine.

Besides the code duplication, all are wrong when the
sc is greater than 15.   In that case the code incorrectly
or's a 1 into the computed sc instead of 1 shifted left
by 4.

Fix precomputed sc5 by using an already implemented routine
hdr2sc() and deleting flawed duplicated code.

Cc: Stable <stable@vger.kernel.org> # 4.6+
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>