staging: comedi: usbdux: tidy up usbdux_ao_insn_read()

Rename the local variable used for the private data pointer to the
comedi "norm".

Remove the unnecessary sanity check of the private data pointer. This
function can only be called is the private data was allocated during
the attach.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/usbdux.c

@@ -1016,26 +1016,21 @@ static int usbdux_ai_insn_read(struct comedi_device *dev,
 	return ret ? ret : insn->n;
 }
 
-/************************************/
-/* analog out */
-
 static int usbdux_ao_insn_read(struct comedi_device *dev,
 			       struct comedi_subdevice *s,
-			       struct comedi_insn *insn, unsigned int *data)
+			       struct comedi_insn *insn,
+			       unsigned int *data)
 {
+	struct usbdux_private *devpriv = dev->private;
+	unsigned int chan = CR_CHAN(insn->chanspec);
 	int i;
-	int chan = CR_CHAN(insn->chanspec);
-	struct usbdux_private *this_usbduxsub = dev->private;
 
-	if (!this_usbduxsub)
-		return -EFAULT;
-
-	down(&this_usbduxsub->sem);
+	down(&devpriv->sem);
 	for (i = 0; i < insn->n; i++)
-		data[i] = this_usbduxsub->out_buffer[chan];
+		data[i] = devpriv->out_buffer[chan];
+	up(&devpriv->sem);
 
-	up(&this_usbduxsub->sem);
-	return i;
+	return insn->n;
 }
 
 static int usbdux_ao_insn_write(struct comedi_device *dev,