scsi: Suppress gcc 7 fall-through warnings reported with W=1

The conclusion of a recent discussion about the new warnings
reported by gcc 7 is that the new warnings reported when building
with W=1 should be suppressed. However, gcc 7 still warns about
fall-through in switch statements when building with W=1. Suppress
these warnings by annotating the SCSI core properly.

See also Linus Torvalds, Lots of new warnings with gcc-7.1.1, 11
July 2017 (https://www.mail-archive.com/linux-media@vger.kernel.org/msg115428.html).

References: commit bd664f6b3e37 ("disable new gcc-7.1.1 warnings for now")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
diff --git a/drivers/scsi/scsi_ioctl.c b/drivers/scsi/scsi_ioctl.c
index b6bf3f29..0a87549 100644
--- a/drivers/scsi/scsi_ioctl.c
+++ b/drivers/scsi/scsi_ioctl.c
@@ -116,13 +116,15 @@ static int ioctl_internal_command(struct scsi_device *sdev, char *cmd,
 		case NOT_READY:	/* This happens if there is no disc in drive */
 			if (sdev->removable)
 				break;
+			/* FALLTHROUGH */
 		case UNIT_ATTENTION:
 			if (sdev->removable) {
 				sdev->changed = 1;
 				result = 0;	/* This is no longer considered an error */
 				break;
 			}
-		default:	/* Fall through for non-removable media */
+			/* FALLTHROUGH -- for non-removable media */
+		default:
 			sdev_printk(KERN_INFO, sdev,
 				    "ioctl_internal_command return code = %x\n",
 				    result);