Decrease kLargeMalloc block size in ASAN unit tests.

Summary:
Make kLargeMalloc big enough to be handled by secondary allocator
and small enough to fit into quarantine for all configurations.
It become too big to fit into quarantine on Android after D27873.

Reviewers: eugenis

Patch by Alex Shlyapnikov.

Subscribers: danalbert, llvm-commits, kubabrecka

Differential Revision: https://reviews.llvm.org/D28142

llvm-svn: 290689