scsi: lpfc: Fix used-RPI accounting problem.

With 255 vports created a link trasition can casue a crash.

When going through discovery after a link bounce the driver is using
rpis before the cmd FCOE_POST_HDR_TEMPLATES completes. By doing that the
next rpi bumps the rpi range out of the boundary.

The fix it to increment the next_rpi only when the
FCOE_POST_HDR_TEMPLATE succeeds.

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