mem: Fix use-after-free bug

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>
1 file changed