lib/test_kmod.c: fix rmmod double free

We free the misc device string twice on rmmod; fix this.  Without this
we cannot remove the module without crashing.

Link: http://lkml.kernel.org/r/20181124050500.5257-1-mcgrof@kernel.org
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org>	[4.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/test_kmod.c

@@ -1214,7 +1214,6 @@ void unregister_test_dev_kmod(struct kmod_test_device *test_dev)
 
 	dev_info(test_dev->dev, "removing interface\n");
 	misc_deregister(&test_dev->misc_dev);
-	kfree(&test_dev->misc_dev.name);
 
 	mutex_unlock(&test_dev->config_mutex);
 	mutex_unlock(&test_dev->trigger_mutex);