mem-ruby: Fix MultiGrainBloomFilter total count calculation

mem-ruby: Fix MultiGrainBloomFilter total count calculation

Previous value was always 0, and was never incrementing. The
total count should take into account the value stored in the
entry.

Change-Id: I93813e3f388198967b30cf11848a8a8c3a7b91f4
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18733
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>