[asan] Increase LocatePcInTrace threshold.

Not sure what changed, but on my machine this is literally one byte
short. Only happens when malloc_context_size <= 2 due to the special
case in GET_STACK_TRACE definition (see asan_stack.h):
StackTrace::GetCurrentPc() on the right (context size > 2) branch
returns the address that is 200-something bytes from the return
address it is later matched to, while the same call on the left
branch is 321 bytes away from it.

This fixes the double-free test on my machine.

llvm-svn: 266932