ide-cd: document capacity hack

Just copy the comment from drivers/scsi/sr.c::sr_done()
(from which the capacity hack has been originated).

Cc: Borislav Petkov <petkovbb@gmail.com>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/ide-cd.c

@@ -194,6 +194,14 @@ static void cdrom_analyze_sense_data(ide_drive_t *drive,
 			bio_sectors = max(bio_sectors(failed_command->bio), 4U);
 			sector &= ~(bio_sectors - 1);
 
+			/*
+			 * The SCSI specification allows for the value
+			 * returned by READ CAPACITY to be up to 75 2K
+			 * sectors past the last readable block.
+			 * Therefore, if we hit a medium error within the
+			 * last 75 2K sectors, we decrease the saved size
+			 * value.
+			 */
 			if (sector < get_capacity(info->disk) &&
 			    drive->probed_capacity - sector < 4 * 75)
 				set_capacity(info->disk, sector);