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

The `insn_write` handler for the AO subdevice (`labpc_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 `labpc_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/ni_labpc_common.c

@@ -906,7 +906,9 @@ static int labpc_ao_insn_write(struct comedi_device *dev,
 {
 	const struct labpc_boardinfo *board = dev->board_ptr;
 	struct labpc_private *devpriv = dev->private;
-	int channel, range;
+	unsigned int channel;
+	unsigned int range;
+	unsigned int i;
 	unsigned long flags;
 
 	channel = CR_CHAN(insn->chanspec);
@@ -932,9 +934,10 @@ static int labpc_ao_insn_write(struct comedi_device *dev,
 		devpriv->write_byte(dev, devpriv->cmd6, CMD6_REG);
 	}
 	/* send data */
-	labpc_ao_write(dev, s, channel, data[0]);
+	for (i = 0; i < insn->n; i++)
+		labpc_ao_write(dev, s, channel, data[i]);
 
-	return 1;
+	return insn->n;
 }
 
 /* lowlevel write to eeprom/dac */