s390/extmem: remove stale -ENOSPC comment and handling

segment_load() will no longer return -ENOSPC. If a segment overlaps with
storage, we now also return -EBUSY. Remove the stale comment from
__segment_load() and the stale handling from segment_warning().

Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200630084240.8283-1-david@redhat.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>