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 <[e-mail]>
Cc: Ben Dooks <[e-mail]>
Signed-off-by: Rusty Russell <[e-mail]>

drivers/video/fbdev/sm501fb.c

···
 }
 
 /* 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
  *