i40iw: Remove variable flush_code and check to set qp->sq_flush

The flush_code variable in i40iw_bld_terminate_hdr() is obsolete and
the check to set qp->sq_flush is unreachable. Currently flush code is
populated in setup_term_hdr() and both SQ and RQ are flushed always
as part of the tear down flow.

Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Henry Orosco <henry.orosco@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>