affs: Replace one-element array with flexible-array member

Replace the deprecated one-element array with a modern flexible-array
member in the struct affs_root_head.

Add a comment that most struct members are not used, but kept as
documentation.

Link: https://github.com/KSPP/linux/issues/79Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/affs/amigaffs.h

@@ -49,12 +49,13 @@ struct affs_short_date {
 
 struct affs_root_head {
 	__be32 ptype;
+	/* The following fields are not used, but kept as documentation. */
 	__be32 spare1;
 	__be32 spare2;
 	__be32 hash_size;
 	__be32 spare3;
 	__be32 checksum;
-	__be32 hashtable[1];
+	__be32 hashtable[];
 };
 
 struct affs_root_tail {