bssgp_fc_test: sanitize: free fc struct when done

Helps fix sanitizer build on debian 9.

Change-Id: I0ef95ee8185a4789f0732b9420243dda5104d181
diff --git a/tests/gb/bssgp_fc_test.c b/tests/gb/bssgp_fc_test.c
index 98e17cc..ac690a5 100644
--- a/tests/gb/bssgp_fc_test.c
+++ b/tests/gb/bssgp_fc_test.c
@@ -104,6 +104,8 @@
 		if (llist_empty(&fc->queue))
 			break;
 	}
+
+	talloc_free(fc);
 }
 
 static void help(void)