Sysace: Don't enable IRQ until after interrupt handler is registered

The previous patch to move the interrupt handler registration moved it
below enabling interrupts which could be a problem if the device is on
a shared interrupt line.  This patch fixes the order.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>