test-aio-multithread: do not use mb_read/mb_set for simple flags

The remaining use of mb_read/mb_set is just to force a thread to exit
eventually.  It does not order two memory accesses and therefore can be
just read/set.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 file changed