Increment pages_freed each time a page was swept. Before pages_freed
was always 0, which meant that the max_pages-argument did not have any
effect.

Change-Id: Id8908bdeb38e262e09b4069893f8f81209568080
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1872399Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64564}