stdio: Fix memleak on stdio_deregister

stdio_register makes a malloc-ed copy of struct stdio_dev through stdio_clone,
free the malloc-ed memory on stdio_deregister.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
diff --git a/common/stdio.c b/common/stdio.c
index 68c595d..adbfc89 100644
--- a/common/stdio.c
+++ b/common/stdio.c
@@ -197,6 +197,7 @@
 	}
 
 	list_del(&(dev->list));
+	free(dev);
 
 	/* reassign Device list */
 	list_for_each(pos, &(devs.list)) {