[PATCH] md: Change the way the name of an md device is printed in error messages.

[PATCH] md: Change the way the name of an md device is printed in error messages.

From: NeilBrown <neilb@cse.unsw.edu.au>

Instead of using ("md%d", mdidx(mddev)), we now use ("%s", mdname(mddev))
where mdname is the disk_name field in the associated gendisk structure.
This allows future flexability in naming.