cciss: cleanup interrupt_not_for_us

cciss: cleanup interrupt_not_for_us
In the case of MSI/MSIX interrutps, we don't need to check
if the interrupt is for us, and in the case of the intx interrupt
handler, when checking if the interrupt is for us, we don't need
to check if we're using MSI/MSIX, we know we're not.

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>