Fix typo in libartbase mem_map.h am: 999465fda7

Original change: https://android-review.googlesource.com/c/platform/art/+/2460088

Change-Id: Ie24dd5268042b066a88fbbfd7b8e15730e6a3703
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>