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 Merged-In: I95fafcf24b9ae821d8b19782813c7b2f312bf317