scsi: sd_zbc: Let the SCSI core handle ILLEGAL REQUEST / ASC 0x21

scsi_io_completion() translates the sense key ILLEGAL REQUEST / ASC 0x21 into
ACTION_FAIL. That means that setting cmd->allowed to zero in sd_zbc_complete()
for this sense code / ASC combination is not necessary. Hence remove the code
that resets cmd->allowed from sd_zbc_complete().

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>