staging: comedi: ni_65xx: Use 16-bit 0 for interrupt data

The ni_65xx 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/20210223143055.257402-14-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ian-abbott

drivers/staging/comedi/drivers/ni_65xx.c

@@ -472,6 +472,7 @@ static irqreturn_t ni_65xx_interrupt(int irq, void *d)
 	struct comedi_device *dev = d;
 	struct comedi_subdevice *s = dev->read_subdev;
 	unsigned int status;
+	unsigned short val = 0;
 
 	status = readb(dev->mmio + NI_65XX_STATUS_REG);
 	if ((status & NI_65XX_STATUS_INT) == 0)
@@ -482,7 +483,7 @@ static irqreturn_t ni_65xx_interrupt(int irq, void *d)
 	writeb(NI_65XX_CLR_EDGE_INT | NI_65XX_CLR_OVERFLOW_INT,
 	       dev->mmio + NI_65XX_CLR_REG);
 
-	comedi_buf_write_samples(s, &s->state, 1);
+	comedi_buf_write_samples(s, &val, 1);
 	comedi_handle_events(dev, s);
 
 	return IRQ_HANDLED;