devlink: use -ENOSPC to indicate no more room for snapshots

The devlink_region_snapshot_create function returns -ENOMEM when the
maximum number of snapshots has been reached. This is confusing because
it is not an issue of being out of memory. Change this to use -ENOSPC
instead.
Reported-by: NJiri Pirko <jiri@resnulli.us>
Signed-off-by: NJacob Keller <jacob.e.keller@intel.com>
Reviewed-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/devlink.c

@@ -3793,7 +3793,7 @@ __devlink_region_snapshot_create(struct devlink_region *region,
 
 	/* check if region can hold one more snapshot */
 	if (region->cur_snapshots == region->max_snapshots)
-		return -ENOMEM;
+		return -ENOSPC;
 
 	if (devlink_region_snapshot_get_by_id(region, snapshot_id))
 		return -EEXIST;