Fix incorrect summary for LE audio hearing aids

For LE audio lead device, the `CachedBluetoothDevice.isConnected()` will return true since `BluetoothLeAudio.getConnectionStatus(device)` will return STATE_CONNECTED even if the device is powered off. Changing to use `CachedBluetoothDevice.getDevice().isConnected()` can avoid the wrong value of the connection status of the device.

Bug: 325524694
Flag: EXEMPT bugfix
Test: atest AccessibilityHearingAidPreferenceControllerTest
Change-Id: If763c0861bb5796d9bc0511916b7077c784b49f5