btl/openib: addition conditional around an assert

A user trying to build Open MPI with explicit use
of CFLAGS on the make command line hit problems.

This fixes one of the problems.

https://www.mail-archive.com/users@lists.open-mpi.org//msg32241.html

Signed-off-by: Howard Pritchard <hppritcha@gmail.com>

opal/mca/btl/openib/btl_openib_component.c

@@ -3436,7 +3436,9 @@ progress_pending_frags_wqe(mca_btl_base_endpoint_t *ep, const int qpn)
             frag = opal_list_remove_first(&ep->qps[qpn].no_wqe_pending_frags[i]);
             if(NULL == frag)
                 break;
+#if OPAL_ENABLE_DEBUG
             assert(0 == frag->opal_list_item_refcount);
+#endif
             tmp_ep = to_com_frag(frag)->endpoint;
             ret = mca_btl_openib_endpoint_post_send(tmp_ep, to_send_frag(frag));
             if (OPAL_SUCCESS != ret) {