raid5: fix duplicate checks for rdev->saved_raid_disk

'first' will always be greater than or equal to 0, it is unnecessary to
repeat the 0 check, clean it up.
Signed-off-by: NJackie Liu <liuyun01@kylinos.cn>
Signed-off-by: NSong Liu <song@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/md/raid5.c

@@ -8263,8 +8263,7 @@ static int raid5_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 	 * find the disk ... but prefer rdev->saved_raid_disk
 	 * if possible.
 	 */
-	if (rdev->saved_raid_disk >= 0 &&
-	    rdev->saved_raid_disk >= first &&
+	if (rdev->saved_raid_disk >= first &&
 	    rdev->saved_raid_disk <= last &&
 	    conf->disks[rdev->saved_raid_disk].rdev == NULL)
 		first = rdev->saved_raid_disk;