Fix some compiler warnings.

As it turns out, we had an overloaded virtual from an earlier era,
with the extra parameter never used.  So cleaning that up was a
bonus to remove the compiler warning.

Change-Id: I780287f8a5d2b0a1ec84ec62c88ba50e051f372b
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

examples/audiodevices/audiodevices.cpp

@@ -58,6 +58,8 @@ QString toString(QAudioFormat::SampleType sampleType)
     case QAudioFormat::Float:
         result = "Float";
         break;
+    case QAudioFormat::Unknown:
+        result = "Unknown";
     }
     return result;
 }