The driver currently keeps local copies of the hardware request/response queue indexes.
But it expends significant effort ensuring consistency between the two views,
and still gets it wrong after an error or reset occurs.

This patch removes the local copies, in favour of just accessing the hardware
whenever we need them.  Eventually this may need to be tweaked again for NCQ,
but for now this works and solves problems some users were seeing.
Signed-off-by: Mark Lord <liml@rtr.ca>
Signed-off-by: Jeff Garzik <jeff@garzik.org>