Fix compile error from ambiguous call to std::abs

webrtc/modules/audio_device/ios/audio_device_ios.mm

Index: webrtc/modules/audio_device/ios/audio_device_ios.mm
diff --git a/webrtc/modules/audio_device/ios/audio_device_ios.mm b/webrtc/modules/audio_device/ios/audio_device_ios.mm
index 3df9c710d782cafcbd999a79295d507a0c8d58f3..f2a3fbbad9ce59b517087e04e98eb14b0f8a40b2 100644
--- a/webrtc/modules/audio_device/ios/audio_device_ios.mm
+++ b/webrtc/modules/audio_device/ios/audio_device_ios.mm
@@ -580,7 +580,7 @@ void AudioDeviceIOS::HandleSampleRateChange(float sample_rate) {
          (unsigned long)current_frames_per_buffer);
 
   // Sample rate and buffer size are the same, no work to do.
-  if (std::abs(current_sample_rate - session_sample_rate) <= DBL_EPSILON &&
+  if (std::abs((int)current_sample_rate - (int)session_sample_rate) <= DBL_EPSILON &&
       current_frames_per_buffer == session_frames_per_buffer) {
     return;
   }