scsi: core: Make the scsi_alloc_sgtables() documentation more accurate

The current scsi_alloc_sgtables() documentation does not accurately explain
what this function does. Hence improve the documentation of this function.

Link: https://lore.kernel.org/r/20210415220826.29438-2-bvanassche@acm.org
Cc: Christoph Hellwig <hch@lst.de>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Daniel Wagner <dwagner@suse.de>
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_lib.c

@@ -999,8 +999,11 @@ static inline bool scsi_cmd_needs_dma_drain(struct scsi_device *sdev,
 }
 
 /**
- * scsi_alloc_sgtables - allocate S/G tables for a command
- * @cmd:  command descriptor we wish to initialize
+ * scsi_alloc_sgtables - Allocate and initialize data and integrity scatterlists
+ * @cmd: SCSI command data structure to initialize.
+ *
+ * Initializes @cmd->sdb and also @cmd->prot_sdb if data integrity is enabled
+ * for @cmd.
  *
  * Returns:
  * * BLK_STS_OK       - on success