RDMA/bnxt_re: remove redundant initialization of rc to zero

rc is initialized to zero but is then updated by calls to
bnxt_qplib_free_fast_reg_page_list and/or bnxt_qpliob_free_mrw
so the initialization is redundant and can be removed.

Detected with CoverityScan, CID#1408448 ("Unused Value")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>