Keep the lock held in getStatusForMetrics()

To avoid inconsistent data, don't release and re-grab the lock in
getStatusForMetrics().

Bug: 245472520
Test: atest
Test: m statsd_testdrive; run "statsd_testdrive 504"
Change-Id: I1ff3f64641543f0b4f87957e9c0ba5a464c6a974