ubi: Fix Fastmap's update_vol()

Usually Fastmap is free to consider every PEB in one of the pools
as newer than the existing PEB. Since PEBs in a pool are by definition
newer than everything else.
But update_vol() missed the case that a pool can contain more than
one candidate.

Cc: <stable@vger.kernel.org>
Fixes: dbb7d2a ("UBI: Add fastmap core")
Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/fastmap.c

@@ -304,6 +304,7 @@ static int update_vol(struct ubi_device *ubi, struct ubi_attach_info *ai,
 			aeb->pnum = new_aeb->pnum;
 			aeb->copy_flag = new_vh->copy_flag;
 			aeb->scrub = new_aeb->scrub;
+			aeb->sqnum = new_aeb->sqnum;
 			ubi_free_aeb(ai, new_aeb);
 
 		/* new_aeb is older */