[libata] wrap kmap_atomic(KM_IRQ0) with local_irq_save/restore()

Interrupts must be disabled if using kmap_atomic(KM_IRQ0), but that was
not the case in a few code paths coming directly from ATA driver
interrupt handlers (which use spin_lock rather than spin_lock_irqsave).

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>