virtiofs: include a newline in sysfs tag

The internal tag string doesn't contain a newline. Append one when
emitting the tag via sysfs.

[Stefan] Orthogonal to the newline issue, sysfs_emit(buf, "%s", fs->tag) is
needed to prevent format string injection.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Fixes: a8f62f50 ("virtiofs: export filesystem tags through sysfs")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/virtio_fs.c

@@ -170,7 +170,7 @@ static ssize_t tag_show(struct kobject *kobj,
 {
 	struct virtio_fs *fs = container_of(kobj, struct virtio_fs, kobj);
 
-	return sysfs_emit(buf, fs->tag);
+	return sysfs_emit(buf, "%s\n", fs->tag);
 }
 
 static struct kobj_attribute virtio_fs_tag_attr = __ATTR_RO(tag);