mem_pkt was deleted (via `delete respQueue.front()`) then used in the following if statement (at `mem_pkt->isDram()`). This patch fixes this issue. Issue-on: https://gem5.atlassian.net/browse/GEM5-1009 Change-Id: Iac3b9078ce5acbdd87a0737a2c98ad887459661f Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/47239 Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br> Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com> Maintainer: Jason Lowe-Power <power.jg@gmail.com> Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com> Tested-by: kokoro <noreply+kokoro@google.com>