mem-ruby: Checkpoint from MOESI_hammer Ruby hangs

mem-ruby: Checkpoint from MOESI_hammer Ruby hangs

Fix MOESI_hammer checkpoint hanging.
The function markRemoved() should be called before hitCallback(),
not after it. The reason is that hitCallback() checks if draining is
complete based on the value of "m_outstanding_count". And since
markRemoved() is responsible for decrementing "m_outstanding_count",
hitCallback() does not see that there are no outstanding requests.

Reported by: Timothy Hayes
Jira: https://gem5.atlassian.net/browse/GEM5-331
Change-Id: I14c34be79843b172ae994ab1792fe4ce6cf5cf6e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/25683
Reviewed-by: Timothy Hayes <timothy.hayes@arm.com>
Reviewed-by: John Alsop <johnathan.alsop@amd.com>
Maintainer: Bradford Beckmann <brad.beckmann@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>