This patch addresses a number of weird behaviours observed
for the sata_mv driver, by fixing an "off by one" bug in processing
of the EDMA response queue.

Basically, sata_mv was looking in the wrong place for
command results, and this produced a lot of unpredictable behaviour.
Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>