fix leak in romfs_fill_super()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/romfs/super.c

@@ -544,6 +544,7 @@ error:
 error_rsb_inval:
 	ret = -EINVAL;
 error_rsb:
+	kfree(rsb);
 	return ret;
 }