btrfs-progs: receive: update unclear error message when processing

Make the message a bit more clear that it's related to the send/receive
use case where the parent subvolume needs to match.

Issue: #1003
Pull-request: #1005
Signed-off-by: David Sterba <dsterba@suse.com>

Author: jschwender

cmds/receive.c

@@ -310,7 +310,7 @@ static int process_snapshot(const char *path, const u8 *uuid, u64 ctransid,
 		else
 			ret = PTR_ERR(parent_subvol);
 		uuid_unparse(parent_uuid, uuid_str);
-		error("snapshot: cannot find parent subvolume %s", uuid_str);
+		error("snapshot receive: cannot find parent subvolume %s", uuid_str);
 		goto out;
 	}