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>

drivers/staging/comedi/drivers/quatech_daqp_cs.c

@@ -214,6 +214,9 @@ static irqreturn_t daqp_interrupt(int irq, void *dev_id)
 		return IRQ_NONE;
 
 	status = inb(dev->iobase + DAQP_STATUS_REG);
+	if (!(status & DAQP_STATUS_EVENTS))
+		return IRQ_NONE;
+
 	while (!(status & DAQP_STATUS_FIFO_EMPTY)) {
 		unsigned short data;