[PATCH] DM9000 - better checks for platform resources

The current DM9000 driver cannot cope if it
is given more than 3 resources (for example, if
it is being passed an wake-up irq that it is
not using yet).

Check that we have been given at-least one IRQ
resource.

Also fix the minor type-casting for the case
of 2 resources.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>