staging: comedi: addi_apci_1564: check INSN_CONFIG_DIGITAL_TRIG shift

commit 926234f1 upstream.

The `INSN_CONFIG` comedi instruction with sub-instruction code
`INSN_CONFIG_DIGITAL_TRIG` includes a base channel in `data[3]`. This is
used as a right shift amount for other bitmask values without being
checked.  Shift amounts greater than or equal to 32 will result in
undefined behavior.  Add code to deal with this.

Fixes: 1e15687e

 ("staging: comedi: addi_apci_1564: add Change-of-State interrupt subdevice and required functions")
Cc: <stable@vger.kernel.org> #3.17+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20200717145257.112660-4-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>