Don't consider disks with a valid recovery offset as candidates for bumping up event...

Don't consider disks with a valid recovery offset as candidates for bumping up event count

When we are looking for a candidate disk to bump up the event count,
we consider only disks that have recovery_start==MaxSector.
However, after we find one such disk, we agree to accept more disks
having same event count, regardless of their recovery_start.
Be consistent and don't accept disks with a valid recovery_start at all.

Signed-off-by: NeilBrown <neilb@suse.de>