Workaround for errata SATA#26.

Prevents accidently putting a drive to sleep when attempting COMRESET,
by ORing 0xf000 with the values written to SCR_CONTROL.
Signed-off-by: NMark Lord <mlord@pobox.com>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>