Replace free and return NULL with return mfree

src/libudev/libudev-hwdb.c

@@ -113,8 +113,7 @@ _public_ struct udev_hwdb *udev_hwdb_unref(struct udev_hwdb *hwdb) {
                 return NULL;
         sd_hwdb_unref(hwdb->hwdb);
         udev_list_cleanup(&hwdb->properties_list);
-        free(hwdb);
-        return NULL;
+        return mfree(hwdb);
 }
 
 /**

src/libudev/libudev-monitor.c

@@ -493,8 +493,7 @@ _public_ struct udev_monitor *udev_monitor_unref(struct udev_monitor *udev_monit
                 close(udev_monitor->sock);
         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
         udev_list_cleanup(&udev_monitor->filter_tag_list);
-        free(udev_monitor);
-        return NULL;
+        return mfree(udev_monitor);
 }
 
 /**

src/libudev/libudev-queue.c

@@ -115,8 +115,7 @@ _public_ struct udev_queue *udev_queue_unref(struct udev_queue *udev_queue)
 
         safe_close(udev_queue->fd);
 
-        free(udev_queue);
-        return NULL;
+        return mfree(udev_queue);
 }
 
 /**

src/libudev/libudev.c

@@ -136,8 +136,7 @@ _public_ struct udev *udev_unref(struct udev *udev) {
         udev->refcount--;
         if (udev->refcount > 0)
                 return udev;
-        free(udev);
-        return NULL;
+        return mfree(udev);
 }
 
 /**