scsi: lpfc: Fix link speed reporting for 4-link trunk

Driver is using uint16_t and is encountering an overflow of the 16bits when
calculating link speed.

Fix by using a u32 type.

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>