staging: comedi: pcl818: Fix endian problem for AI command data

The analog input subdevice supports Comedi asynchronous commands that
use Comedi's 16-bit sample format.  However, the call to
`comedi_buf_write_samples()` is passing the address of a 32-bit integer
parameter.  On bigendian machines, this will copy 2 bytes from the wrong
end of the 32-bit value.  Fix it by changing the type of the parameter
holding the sample value to `unsigned short`.

[Note: the bug was introduced in commit edf4537 ("staging: comedi:
pcl818: use comedi_buf_write_samples()") but the patch applies better to
commit d615416 ("staging: comedi: pcl818: introduce
pcl818_ai_write_sample()").]

Fixes: d615416 ("staging: comedi: pcl818: introduce pcl818_ai_write_sample()")
Cc: <stable@vger.kernel.org> # 4.0+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20210223143055.257402-10-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ian-abbott

drivers/staging/comedi/drivers/pcl818.c

@@ -423,7 +423,7 @@ static int pcl818_ai_eoc(struct comedi_device *dev,
 
 static bool pcl818_ai_write_sample(struct comedi_device *dev,
 				   struct comedi_subdevice *s,
-				   unsigned int chan, unsigned int val)
+				   unsigned int chan, unsigned short val)
 {
 	struct pcl818_private *devpriv = dev->private;
 	struct comedi_cmd *cmd = &s->async->cmd;