staging: comedi: addi_apci_1032: check shared interrupt

In the interrupt service routine, check the device is asserting the
shared interrupt line and check that interrupts have been enabled.

When attaching the device, disable interrupts before setting up the
interrupt handler to avoid handling spurious interrupts before the
device is ready.

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