bootstat: fix test regression (extra logging)

Deal with regression from 9a3870490a005ac73dc1e2be202e0824cc239e43
where additional content is logged and should be ignored.

Test: system/core/bootstat/boot_reason_test.sh
Bug: 63736262
Change-Id: I70709ba5b00ea18a653ff8d1658556b7d4c48775
1 file changed