scsi: fc: provide fc_bsg_to_shost() helper

Provide fc_bsg_to_shost() helper that will become handy when we're
moving from struct fc_bsg_job to a plain struct bsg_job. Also use this
little helper in the LLDDs.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Acked-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>