scsi: lpfc: Correct errors accessing fw log

This patch corrects two issues:

- An oops would occur if reading based on a non-zero offset.  Offset
  calculation was incorrect.

- Updates to ras config (logging level) were ignored if change was
  made while fw logging was enabled. Revise to dynamically update.

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