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>