staging: comedi: comedi_parport: Use 16-bit 0 for interrupt data

The comedi_parport driver has an "interrupt" subdevice that supports
Comedi asynchronous commands, placing a value in the Comedi buffer for
each interrupt.  The subdevice uses Comedi's 16-bit sample format but
the interrupt handler is calling `comedi_buf_write_samples()` with the
address of a 32-bit integer `&s->state`.  On bigendian machines, this
will copy 2 bytes from the wrong end of the 32-bit integer.  This isn't
really a problem since `s->state` will always be 0 for this subdevice,
but clean it up by using a 16-bit variable initialized to 0 to pass the
value.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20210223143055.257402-12-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ian-abbott

drivers/staging/comedi/drivers/comedi_parport.c

@@ -210,12 +210,13 @@ static irqreturn_t parport_interrupt(int irq, void *d)
 	struct comedi_device *dev = d;
 	struct comedi_subdevice *s = dev->read_subdev;
 	unsigned int ctrl;
+	unsigned short val = 0;
 
 	ctrl = inb(dev->iobase + PARPORT_CTRL_REG);
 	if (!(ctrl & PARPORT_CTRL_IRQ_ENA))
 		return IRQ_NONE;
 
-	comedi_buf_write_samples(s, &s->state, 1);
+	comedi_buf_write_samples(s, &val, 1);
 	comedi_handle_events(dev, s);
 
 	return IRQ_HANDLED;