sata_sil24: Identify which card suffered IRQ status error

In machines with multiple Silicon Image 3124 and/or 3132 cards, there is no
way to tell which card is the culprit when the sata_sil24 interrupt handler
gets a bad status.

Tested-by: Tim Small <tim@seoss.co.uk>
Signed-off-by: Tim Small <tim@seoss.co.uk>
Signed-off-by: Tejun Heo <tj@kernel.org>