sd: retry discard commands

Currently cmd->allowed is initialized from rq->retries for discard
commands, but retries is always 0 for non-BLOCK_PC requests.  Set it
to the standard number of retries instead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>

drivers/scsi/sd.c

@@ -758,7 +758,7 @@ static int sd_setup_discard_cmnd(struct scsi_cmnd *cmd)
 	rq->timeout = SD_TIMEOUT;
 
 	cmd->transfersize = len;
-	cmd->allowed = rq->retries;
+	cmd->allowed = SD_MAX_RETRIES;
 
 	/*
 	 * Initially __data_len is set to the amount of data that needs to be