scsi: remove abuses of scsi_populate_tag

Unless we want to build a SPI tag message we should just check SCMD_TAGGED
instead of reverse engineering a tag type through the use of
scsi_populate_tag_msg.

Also rename the function to spi_populate_tag_msg, make it behave like the
other spi message helpers, and move it to the spi transport class.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Reviewed-by: Hannes Reinecke <hare@suse.de>

drivers/scsi/esp_scsi.c

@@ -663,7 +663,7 @@ static struct esp_cmd_entry *find_and_prep_issuable_command(struct esp *esp)
 			return ent;
 		}
 
-		if (!scsi_populate_tag_msg(cmd, &ent->tag[0])) {
+		if (!spi_populate_tag_msg(&ent->tag[0], cmd)) {
 			ent->tag[0] = 0;
 			ent->tag[1] = 0;
 		}