Add comment for AudioManager.getDevices.

Currently, audio framework only supports connecting one device per
device type. It will be good to state this limitation in the API to
query available devices.

Bug: 255248910
Test: make
Change-Id: I2f0c08c411d02a31cf2e8282ecf4226dcdf2444a

media/java/android/media/AudioManager.java

@@ -6898,6 +6898,10 @@ public class AudioManager {
      * Returns an array of {@link AudioDeviceInfo} objects corresponding to the audio devices
      * currently connected to the system and meeting the criteria specified in the
      * <code>flags</code> parameter.
+     * Notes that Android audio framework only support one device per device type. In that case,
+     * if there are multiple audio device with the same device type connected to the Android device,
+     * only the last reported device will be known by Android audio framework and returned by this
+     * API.
      * @param flags A set of bitflags specifying the criteria to test.
      * @see #GET_DEVICES_OUTPUTS
      * @see #GET_DEVICES_INPUTS