Fix a signed-unsigned comparison.

RtAudio.cpp

@@ -9113,7 +9113,7 @@ bool RtApiOss :: probeDeviceOpen( unsigned int device, StreamMode mode, unsigned
   }
 
   // Verify the sample rate setup worked.
-  if ( abs( srate - sampleRate ) > 100 ) {
+  if ( abs( srate - (int)sampleRate ) > 100 ) {
     close( fd );
     errorStream_ << "RtApiOss::probeDeviceOpen: device (" << ainfo.name << ") does not support sample rate (" << sampleRate << ").";
     errorText_ = errorStream_.str();