MidiBluetoothService: add new device to HashMap

The HashMap is being used but devices never added to the map.

Bug: 23429459
Change-Id: I1da5305a56f5bd48e1c5d9345e721ea8dd2eed4e
Signed-off-by: Phil Burk <philburk@google.com>
(cherry picked from commit e5f722e5)

media/packages/BluetoothMidiService/src/com/android/bluetoothmidiservice/BluetoothMidiService.java

@@ -46,6 +46,7 @@ public class BluetoothMidiService extends Service {
                 device = mDeviceServerMap.get(bluetoothDevice);
                 if (device == null) {
                     device = new BluetoothMidiDevice(this, bluetoothDevice, this);
+                    mDeviceServerMap.put(bluetoothDevice, device);
                 }
             }
             return device.getBinder();