Fix pairing dialog doesn't show the correct pairing key.

When the pairing dialog doesn't show in the foreground at the first time, the pairing key will display incorrectly.
This is caused by the intent doesn't contain the parameter BluetoothDevice.EXTRA_PAIRING_KEY.

Correct the pairing key by passing the pairing key to intent pairingDialogIntent.

Tag: #stability
Bug: 188614067
Test: make RunSettingsRoboTests ROBOTEST_FILTER=BluetoothPairingServiceTest
Change-Id: I3c91bf6ea51fa3fb77b4c4a5c17555606160603e