scsi: Remove one useless stack variable

The local variable of 'devname' in scsi_report_lun_scan() isn't used any
more, so remove it.

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>