systemc,util: Fix a bad port of a change from gem5 proper to here.

This change:

systemc: remove pipe through flag in TLM extension

applied a change from gem5 proper in the gem5/TLM bridge improperly
here, adding a reference to a member variable that didn't exist. This
change removes the extra and invalid level of indirection to get things
to build again.

Change-Id: I77ffdb5408525e116d414df2095a944c58e40b4d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42586
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Earl Ou <shunhsingou@google.com>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

util/tlm/src/sc_slave_port.cc

@@ -301,7 +301,7 @@ SCSlavePort::pec(
             packet->makeResponse();
         }
         if (packet->isResponse()) {
-            need_retry = !bridgeResponsePort.sendTimingResp(packet);
+            need_retry = !sendTimingResp(packet);
         }
 
         if (need_retry) {