Staging: comedi: clean up conditional statement in addi_apci_3xxx.c

In this conditional statement, if (chan < 16), but the instruction passed
in data[0] is INSN_CONFIG_DIO_QUERY, the function does not return early,
but the else-branch does not get executed either.  As a result, mask
would be used uninitialized in the next line.  We want
comedi_dio_insn_config() to use a chan_mask based on the chanspec for the
INSN_CONFIG_DIO_QUERY instruction, so mask should be initialized to 0.
Then, if instead the instruction is INSN_CONFIG_DIO_{INPUT,OUTPUT}, we
return an error if (chan < 16) as these are invalid instructions for
ports 0 and 1, or update the mask otherwise, so all the io_bits are
modified for port 2.  This ensures that mask is always initialized by the
time it is used.

Signed-off-by: Chase Southwood <chase.southwood@yahoo.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/addi_apci_3xxx.c

@@ -680,7 +680,7 @@ static int apci3xxx_dio_insn_config(struct comedi_device *dev,
 				    unsigned int *data)
 {
 	unsigned int chan = CR_CHAN(insn->chanspec);
-	unsigned int mask;
+	unsigned int mask = 0;
 	int ret;
 
 	/*
@@ -688,12 +688,13 @@ static int apci3xxx_dio_insn_config(struct comedi_device *dev,
 	 * Port 1 (channels 8-15) are always outputs
 	 * Port 2 (channels 16-23) are programmable i/o
 	 */
-	if (chan < 16) {
-		if (data[0] != INSN_CONFIG_DIO_QUERY)
+	if (data[0] != INSN_CONFIG_DIO_QUERY) {
+		/* ignore all other instructions for ports 0 and 1 */
+		if (chan < 16)
 			return -EINVAL;
-	} else {
-		/* changing any channel in port 2 changes the entire port */
-		mask = 0xff0000;
+		else
+			/* changing any channel in port 2 changes the entire port */
+			mask = 0xff0000;
 	}
 
 	ret = comedi_dio_insn_config(dev, s, insn, data, mask);