scsi: Fix wrong additional sense length in descriptor format

The sense header additional sense length should be the accumulated
size of all the descriptors. Information descriptor size is 12 bytes.
When setting the additional sense length we should add 0xc instead of
0xa.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>