audioflinger: Adjust throttle interval when effects in use

 * Loud clicks/pops are heard when playing to a USB device with
   AudioFX enabled. Particularly frequent when the USB device is
   capable of high-resolution output.
 * Adjust the throttling period when effects are enabled to
   prevent this.

Change-Id: I3db220d13c37f4ff5b835c14831fbe6f5a5b062c