scsi: snic: Remove code that zeroes driver-private command data

Since the SCSI core zeroes driver-private command data, remove that code
from the snic driver.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Narsimhulu Musini <nmusini@cisco.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Sesidhar Baddela <sebaddel@cisco.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>