Use mFrameSize instead of mBitShift

Change-Id: Idac335ae70cc9300bb3325839fe8ef1e9e097245
diff --git a/include/media/nbaio/AudioStreamInSource.h b/include/media/nbaio/AudioStreamInSource.h
index 07d8c89..eaea63c 100644
--- a/include/media/nbaio/AudioStreamInSource.h
+++ b/include/media/nbaio/AudioStreamInSource.h
@@ -43,7 +43,7 @@
 
     // This is an over-estimate, and could dupe the caller into making a blocking read()
     // FIXME Use an audio HAL API to query the buffer filling status when it's available.
-    virtual ssize_t availableToRead() { return mStreamBufferSizeBytes >> mBitShift; }
+    virtual ssize_t availableToRead() { return mStreamBufferSizeBytes / mFrameSize; }
 
     virtual ssize_t read(void *buffer, size_t count);