Fix inequality typo in StreamIn::getCapturePosition

This was preventing getCapturePosition() being called from
the default HIDL implementation.

Test: cts-tradefed run cts -m CtsMediaTestCases \
      -t android.media.cts.AudioRecordTest
Change-Id: I9c920108f68fb895a7f7a9d2ea27c291a91c1afb