md: limit mdstat resync progress to max_sectors

There is a small window near the end of md_do_sync where mddev->curr_resync
can be equal to MaxSector.

If status_resync is called during this window, the resulting /proc/mdstat
output contains a HUGE number of = signs due to the very large curr_resync:

Personalities : [raid1]
md123 : active raid1 sdd3[2] sdb3[0]
  204736 blocks super 1.0 [2/1] [U_]
  [=====================================================================
   ... (82 MB more) ...
   ================>]  recovery =429496729.3% (9223372036854775807/204736)
   finish=0.2min speed=12796K/sec
  bitmap: 0/1 pages [0KB], 65536KB chunk

Modify status_resync to ensure the resync variable doesn't exceed
the array's max_sectors.
Signed-off-by: Nate Dailey <nate.dailey@stratus.com>
Acked-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/md.c

@@ -7605,7 +7605,9 @@ static int status_resync(struct seq_file *seq, struct mddev *mddev)
 		if (test_bit(MD_RECOVERY_DONE, &mddev->recovery))
 			/* Still cleaning up */
 			resync = max_sectors;
-	} else
+	} else if (resync > max_sectors)
+		resync = max_sectors;
+	else
 		resync -= atomic_read(&mddev->recovery_active);
 
 	if (resync == 0) {