HWAsan: Increase the malloc fill size.

To match the scudo allocator's always return zero allocation behavior,
set the max malloc fill size larger than the largest size class.
Currently, the largest is 65552, so set the max to 128KB to avoid
needing to change this in the future.

Test: Run test that verifies allocations returned are zero and it passes.
Change-Id: Ie9f0b0d54f846008b1c6d5dc6e55c7031262d29e