unifying: Disable if the kernel has no CONFIG_HIDRAW support

Fixes: https://github.com/hughsie/fwupd/issues/235

plugins/unifying/fu-plugin-unifying.c

@@ -278,6 +278,17 @@ gboolean
 fu_plugin_startup (FuPlugin *plugin, GError **error)
 {
 	FuPluginData *data = fu_plugin_get_data (plugin);
+
+	/* check the kernel has CONFIG_HIDRAW */
+	if (!g_file_test ("/sys/class/hidraw", G_FILE_TEST_IS_DIR)) {
+		g_set_error_literal (error,
+				     FWUPD_ERROR,
+				     FWUPD_ERROR_NOT_SUPPORTED,
+				     "no kernel support for CONFIG_HIDRAW");
+		return FALSE;
+	}
+
+	/* coldplug */
 	g_signal_connect (data->ctx, "added",
 			  G_CALLBACK (fu_plugin_unifying_device_added_cb),
 			  plugin);