staging: comedi: pcl816: exit interrupt quick when there is nothing to do

staging: comedi: pcl816: exit interrupt quick when there is nothing to do

If an async ai command is not running or the int816_mode is 0 the
interrupt routine doesn't do anything other than spew some noise and
clear the interrupt request in the hardware.

Because this driver is manually attached, the "premature interrupt"
check in the interrupt handler should never happen. The interrupt is
only hooked up during the attach and it's released during the detach.

Combine these checks so that the interrupt function exits quick if it
has nothing to handle. Remove the noise.

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>