Switch to using 0 instead of NULL for a void* -> int cast am: 4f98785e4d am: 0466ec5978 am: 824590ace9

Original change: https://android-review.googlesource.com/c/platform/system/memory/libion/+/1362817

Change-Id: I537d0d911f53d751d73f2e8720868daf5fa5e5d4