sim-se: small performance optimization

sim-se: small performance optimization

A local variable was being set inside a loop when it should
have been set outside the loop. This changeset moves the
variable to the appropriate place.

Change-Id: If7655b501bd819c39d35dea4c316b4b9ed3173a2
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17108
Maintainer: Brandon Potter <Brandon.Potter@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>