mem-cache: Fix DCPT with CircularQueue

mem-cache: Fix DCPT with CircularQueue

This patch fixes the following bugs:

- Previously when deltaPointer was 0 or 1, getting the last or penultimate deltas
  would be wrong for non-pow2 deltas.size(). For example, if the last added delta
  was to position 0, the previous should be in position 19, if deltas.size() = 20.
  However, 0-1=4294967295, and 4294967295%20=15.

- When searching for the previous late and penultimate, the oldest entry was being
  skipped.

Change-Id: Id800b60b77531ac4c2920bb90c15cc8cebb137a9
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24538
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Javier Bueno Hedo <javier.bueno@metempsy.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>