scsi: pm80xx: corrected linkrate value.

Corrected the value defined for LINKRATE_60 (6 Gig).

Signed-off-by: Raj Dinesh <Raj.Dinesh@microsemi.com>
Signed-off-by: Viswas G <viswas.g@microsemi.com>
Acked-by: Jack Wang <jinpu.wang@profitbricks.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>