[OpenMP] Make bug49334.cpp more reproducible

`bug49334.cpp` cannot detect data race in `libomptarget` efficiently. It
is reported that with `N = 256` and `BS = 16`, the data race can be reproduced
more steadily. The next coming pathces will fix it so this patch is expected to
fail now.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D104552