UBI: Fix debug message

We have to use j instead of i. i is the volume id
and not the block.

CRs-Fixed: 975289
Change-Id: Ief5f200caf128edfcccdcd19df12b109b8f92fc9
Reported-by:  <Alexander.Block@continental-corporation.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Git-commit: 5347417e56b68354faf315ca42c99cfb0c02f1dd
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Nikhilesh Reddy <reddyn@codeaurora.org>