Fix ineffective assignment.
Fix ineffective assignment.

Signed-off-by: Alexey Palazhchenko <598a0dd5ad1c22a8b1028f205417754164a55ac7@gmail.com>

Gouthamve/prometheus,alileza/prometheus,prometheus/prometheus,prometheus/tsdb,kangwoo/prometheus,kangwoo/prometheus,keegancsmith/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/tsdb,kangwoo/prometheus,prometheus/prometheus,prometheus/prometheus,Gouthamve/prometheus,keegancsmith/prometheus,alileza/prometheus,alileza/prometheus,Gouthamve/prometheus,prometheus/prometheus,Gouthamve/prometheus,alileza/prometheus