sata_mv: workaround errata SATA#26

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: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>