scsi: Define the COMPLETED sense key

Add the definition for the COMPLETED sense key in scsi_proto.h. While at
it, cleanup the white lines around the sense keys macro definitions.

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>