dm persistent data: improve improve space map block alloc failure message

Improve space map error message when unable to allocate a new
metadata block.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/persistent-data/dm-space-map-metadata.c b/drivers/md/persistent-data/dm-space-map-metadata.c
index e89ae5e..906cf3d 100644
--- a/drivers/md/persistent-data/dm-space-map-metadata.c
+++ b/drivers/md/persistent-data/dm-space-map-metadata.c
@@ -337,7 +337,7 @@
 {
 	int r = sm_metadata_new_block_(sm, b);
 	if (r)
-		DMERR("out of metadata space");
+		DMERR("unable to allocate new metadata block");
 	return r;
 }