staging: comedi: quatech_daqp_cs: handle shared interrupt

This is a PCMCIA driver and interrupts are always shared. Detect if
the hardware did not produce the interrupt and return IRQ_NONE so
that other drivers might handle it.

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