[Bluetooth] Handle return values from driver core functions

Some return values of the driver core register and create functions
are not handled and so might cause unexpected problems.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index 7714a2e..14b0f69 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -967,7 +967,8 @@
 		goto error;
 	}
 
-	class_create_file(bt_class, &class_attr_sco);
+	if (class_create_file(bt_class, &class_attr_sco) < 0)
+		BT_ERR("Failed to create SCO info file");
 
 	BT_INFO("SCO (Voice Link) ver %s", VERSION);
 	BT_INFO("SCO socket layer initialized");