ide: repair PIO transfers for cases where nsector > 1

ide: repair PIO transfers for cases where nsector > 1

Currently, for emulated PIO transfers through the AHCI device,
any attempt made to request more than a single sector's worth
of data will result in the same sector being transferred over
and over.

For example, if we request 8 sectors via PIO READ SECTORS, the
AHCI device will give us the same sector eight times.

This patch adds offset tracking into the PIO pathways so that
we can fulfill these requests appropriately.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1414785819-26209-2-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>