fs/adfs: add helper to get discrecord from map

Add a helper to get the disc record from the map, rather than open
coding this in adfs_fill_super().

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/adfs/adfs.h

@@ -1,4 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/buffer_head.h>
 #include <linux/fs.h>
 #include <linux/adfs_fs.h>
 
@@ -18,8 +19,6 @@
 
 #include "dir_f.h"
 
-struct buffer_head;
-
 /*
  * adfs file system inode data in memory
  */
@@ -195,3 +194,10 @@ __adfs_block_map(struct super_block *sb, unsigned int object_id,
 
 	return adfs_map_lookup(sb, object_id >> 8, block);
 }
+
+/* Return the disc record from the map */
+static inline
+struct adfs_discrecord *adfs_map_discrecord(struct adfs_discmap *dm)
+{
+	return (void *)(dm[0].dm_bh->b_data + 4);
+}