Instead of registering one interrupt handler for all four SBUS Quattro
HMEs, let each HME register its own handler. To make this work, we don't
handle the IRQ if none of the status bits are set. This reduces the
complexity of the driver, and makes it easier to ensure things happen
before/after enabling IRQs.

I'm not really sure why we request IRQs in two different places (and leave
them running after removing the driver!). A lot of things in this driver
seem to just be crusty, and not necessarily intentional. I'm assuming
that's the case here as well.

This really needs to be tested by someone with an SBUS Quattro card.
Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>