simpleperf: Fix default value for --etm-flush-interval

options.PullUintValue() returns true even when --etm-flush-interval
isn't used. In this case, interval is still set to etm_flush_interval_,
which makes it 0.

Bug: 336375740
Test: run simpleperf manually
Change-Id: I95fafcf24b9ae821d8b19782813c7b2f312bf317
1 file changed