FIX: imsm: Do not change serial if disk failed

FIX: imsm: Do not change serial if disk failed

This patch rollback one change connected with mdadm-OROM
compatibility:
adding ':0' at the end of disk serial number if disk is
detected as failed.
Current mdadm's implementation does not distinguish two
cases when disk is marked as failed:
1. If disk is really failed- disconnected, broken
2. Just marked as failed by mdadm- using "-f" option

Second case is not yet fully handled and compatible with
IMSM standard.
Changing serial number of existing, operational disk causes
problems in "thunderdome" and "load_super" functions that use
serial numbers to disks comparisons and searching.
The change must be recalled until full support will be
developed.

Signed-off-by: Krzysztof Wojcik <krzysztof.wojcik@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>