scsi: lpfc: Fix null ptr oops updating lpfc_devloss_tmo via sysfs attribute

If an admin updates lpfc's devloss_tmo sysfs attribute, the kernel will
oops.

Coding of a loop allowed a new value (rport) to be set/checked for null
followed by an older value (remoteport) checked for null to allow progress
where the new value, even though null, will be referenced.

Rework the logic to validate and prevent any reference to the null ptr.

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>