Fix IDE DIAGNOSE for packet devices (Vincent Sanders)

Fix IDE DIAGNOSE for packet devices (Vincent Sanders)

The DIAGNOSE command in the qemu IDE implementation has an error when
use dfor packet devices.

The status register value is dependant on the drive being a packet
device or not, this patch corrects the returned status.

From the ATA/PI specification (V6 draft):

"If the device implements the PACKET command feature set, the device
SHALL clear bits 6,5,4,3,2 and 0 in the Status register to zero."

A selection of physical devices have been checked and do conform to
the specifications behaviour.

Signed-off-by: Vincent Sanders <vince@simtec.co.uk>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5452 c046a42c-6fe2-441c-8c8c-71466251a162