uint16_t isn't enough to hold the real sector count, since a value of
zero implies a full 64K sectors, so we need a uint32_t here.

We *could* cheat and pretend that this value is 0-based and fit it in
a uint16_t, but I'd rather waste 2 bytes instead of a future dev's
10 minutes when they forget to +1/-1 accordingly somewhere.

See SATA 3.2, section 13.6.4.1 "READ FPDMA QUEUED".

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1435767578-32743-9-git-send-email-jsnow@redhat.com