staging: comedi: cb_pcidda: Use insn->n in AO insn_write handler

The `insn_write` handler for the AO subdevice
(`cb_pcidda_ao_insn_write()`) currently ignores `insn->n` (the number of
samples to write) and assumes a single sample is to be written.  But
`insn->n` could be 0, meaning no samples should be written, in which
case `data[0]` is invalid.

Follow the usual Comedi guidelines and change
`cb_pcidda_ao_insn_write()` to write the specified number of samples.
This fixes the assumption that `data[0]` is valid.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/cb_pcidda.c

@@ -291,6 +291,7 @@ static int cb_pcidda_ao_insn_write(struct comedi_device *dev,
 	unsigned int channel = CR_CHAN(insn->chanspec);
 	unsigned int range = CR_RANGE(insn->chanspec);
 	unsigned int ctrl;
+	unsigned int i;
 
 	if (range != devpriv->ao_range[channel])
 		cb_pcidda_calibrate(dev, channel, range);
@@ -317,7 +318,8 @@ static int cb_pcidda_ao_insn_write(struct comedi_device *dev,
 
 	outw(ctrl, devpriv->daqio + CB_DDA_DA_CTRL_REG);
 
-	outw(data[0], devpriv->daqio + CB_DDA_DA_DATA_REG(channel));
+	for (i = 0; i < insn->n; i++)
+		outw(data[i], devpriv->daqio + CB_DDA_DA_DATA_REG(channel));
 
 	return insn->n;
 }