fixed below checkpatch warning.
- WARNING: Prefer netdev_warn(netdev, ... then dev_warn(dev, ... then pr_warn(...  to printk(KERN_WARNING ...
Signed-off-by: YAMANE Toshiaki <yamanetoshi@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 
        retval = comedi_buf_write_alloc(async, num_bytes);
        if (retval != num_bytes) {
-               printk(KERN_WARNING "comedi: buffer overrun\n");
+               dev_warn(subd->device->class_dev, "comedi: buffer overrun\n");
                async->events |= COMEDI_CB_OVERFLOW;
                return 0;
        }