bdi: fix -Wformat-security

mm/backing-dev.c:810:57: warning: format string is not a string literal (potentially insecure) [-Wformat-security]

dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);
                                                       ^~~~~~~~~~~~~

---
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 mm/backing-dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 408d5051d05b..5755578d671d 100644
@@ -807,7 +807,7 @@ int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
 		return 0;
 
 	vsnprintf(bdi->dev_name, sizeof(bdi->dev_name), fmt, args);
-	dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);
+	dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, "%s", bdi->dev_name);
 	if (IS_ERR(dev))
 		return PTR_ERR(dev);
 

2.25.1

The callers never pass format strings here. That being said the fix is probably ok anyway, modulo the obvious style issue.