staging: comedi: addi_apci_1500: fix array access out of bounds error

staging: comedi: addi_apci_1500: fix array access out of bounds error

The private data 'pm', 'pt', and 'pp' array members hold the trigger mode
parameters for ports A and B. Both ports are 8-bits and the arrays are 16-bits.
Array index 0 defines the AND mode and index 1 the OR mode parameters for both
ports.

The valid triggers to start the async command are 0 to 3 which select the
AND/OR mode for each port.

The 'pb_trig' (the array index for port B) in apci1500_di_inttrig_start() is
incorrect and results in an index of 0 or 2. Fix the calc so that the correct
index (0/1) is used.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reported-by: Asaf Vertz <asaf.vertz@tandemg.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>