drivers/video/fbdev/sm501fb.c: avoid world-writable sysfs files.

In line with practice for module parameters, we're adding a build-time
check that sysfs files aren't world-writable.

Cc: Vincent Sanders <vince@simtec.co.uk>
Cc: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/video/fbdev/sm501fb.c

@@ -1215,7 +1215,7 @@ static ssize_t sm501fb_crtsrc_store(struct device *dev,
 }
 
 /* Prepare the device_attr for registration with sysfs later */
-static DEVICE_ATTR(crt_src, 0666, sm501fb_crtsrc_show, sm501fb_crtsrc_store);
+static DEVICE_ATTR(crt_src, 0664, sm501fb_crtsrc_show, sm501fb_crtsrc_store);
 
 /* sm501fb_show_regs
  *