scsi: lpfc: Fix reported physical link speed on a disabled trunked link

GetTrunkInfo is displaying an incorrect link speed when the link is a trunk
and the link has gone down.  The driver is not clearing the logical speed
as part of the link down transition.

Fix by setting the logical speed to UNKNOWN SPEED when the link goes down.

Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>