sata_mv: Fix chip type for Hightpoint RocketRaid 1740/1742

Fix chip type for the Highpoint RocketRAID 1740 and 1742 PCI cards.
These really do have Marvell 6042 chips on them, rather than the 5081 chip.

Confirmed by multiple (two) users (for the 1740), and by examining
the product photographs from Highpoint's web site.

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