Fix device creation error response when powered off

When the adapter is powered off the Create*Device methods should fail
early instead of attempting to create a connection in vain.
diff --git a/src/adapter.c b/src/adapter.c
index 2fde7bd..dc2c047 100644
--- a/src/adapter.c
+++ b/src/adapter.c
@@ -1725,6 +1725,9 @@
 	if (check_address(address) < 0)
 		return btd_error_invalid_args(msg);
 
+	if (!adapter->up)
+		return adapter_not_ready(msg);
+
 	if (adapter_find_device(adapter, address))
 		return btd_error_already_exists(msg);
 
@@ -1797,6 +1800,9 @@
 	if (check_address(address) < 0)
 		return btd_error_invalid_args(msg);
 
+	if (!adapter->up)
+		return adapter_not_ready(msg);
+
 	sender = dbus_message_get_sender(msg);
 	if (adapter->agent &&
 			agent_matches(adapter->agent, sender, agent_path)) {