chore(libs): fix -Werror=unused-variable

otherwise test will give wrong result if compiler has -Werror flags,
complained with:

  error: unused variable 'g_ppm_class' [-Werror=unused-variable]

Signed-off-by: Z. Liu <[email protected]>

driver/configure/CLASS_CREATE_1/test.c

@@ -21,6 +21,7 @@ MODULE_AUTHOR("the Falco authors");
 
 static int class_create_test_init(void) {
 	struct class *g_ppm_class = class_create("test");
+	(void)g_ppm_class;
 	return 0;
 }