staging: comedi: addi_apci_2032: make insn_bits read live data

The `insn_bits` handler for the special digital input subdevice used for
interrupts currently uses `s->state` for the data value, which is set to
the value of the APCI2032_INT_STATUS_REG register when a valid interrupt
occurs.  Just read the live register contents in the `insn_bits` handler
instead of relying on the interrupt service routine to read it for us.

The register contains a couple of hardware error status bits.  They
might also be valid even when the corresponding bits have not been
enabled in the APCI_INT_CTRL_REG register in which case this would be
useful for checking for hardware errors without using interrupts, but
this needs to be checked.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>