libata-sff: fix HSM_ST_ERR handling in __ata_sff_port_intr()

While separating out BMDMA irq handler from SFF, commit c3b28894
(libata-sff: separate out BMDMA irq handler) incorrectly made
__ata_sff_port_intr() consider an IRQ to be an idle one if the host
state was transitioned to HSM_ST_ERR by ata_bmdma_port_intr().

This makes BMDMA drivers ignore IRQs reporting host bus error which
leads to timeouts instead of triggering EH immediately.  Fix it by
making __ata_sff_port_intr() consider the IRQ to be an idle one iff
the state is HSM_ST_IDLE.  This is equivalent to adding HSM_ST_ERR to
the "break"ing case but less error-prone.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Antonio Toma <antonio.toma@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>