counters: Fix CounterStateProviderTest sonar issue

Make this non-reused 'fSsb' field an actual local (only) variable.

Change-Id: I50d6af29d2a5a92e601c0141073f0ca9aaa79090
Signed-off-by: Marco Miller <marco.miller@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/c/tracecompass/org.eclipse.tracecompass/+/196398
Tested-by: Trace Compass Bot <tracecompass-bot@eclipse.org>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>

analysis/org.eclipse.tracecompass.analysis.counters.core.tests/src/org/eclipse/tracecompass/analysis/counters/core/tests/CounterStateProviderTest.java

@@ -47,7 +47,6 @@ public class CounterStateProviderTest {
     private static final String COUNTER_FILE = "traces/counter_testTrace.xml";
 
     private TmfXmlTraceStubNs fTrace;
-    private ITmfStateSystemBuilder fSsb;
     private CounterStateProvider fStateProvider;
 
     /**
@@ -79,8 +78,8 @@ public boolean isCumulative() {
         // Create the state provider
         fStateProvider = CounterStateProvider.create(trace);
         IStateHistoryBackend backend = StateHistoryBackendFactory.createInMemoryBackend("CounterStateSystem", 0);
-        fSsb = StateSystemFactory.newStateSystem(backend);
-        fStateProvider.assignTargetStateSystem(fSsb);
+        ITmfStateSystemBuilder ssb = StateSystemFactory.newStateSystem(backend);
+        fStateProvider.assignTargetStateSystem(ssb);
         fTrace = trace;
     }