switch fat to ->s_d_op, close exportfs races there

don't bother with lock_super() in fat_fill_super() callers, while
we are at it - there won't be any concurrency anyway.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index d75a77f..f504089 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -319,7 +319,8 @@
 			struct msdos_dir_entry *de, loff_t i_pos);
 extern int fat_sync_inode(struct inode *inode);
 extern int fat_fill_super(struct super_block *sb, void *data, int silent,
-			const struct inode_operations *fs_dir_inode_ops, int isvfat);
+			const struct inode_operations *fs_dir_inode_ops,
+			int isvfat, void (*setup)(struct super_block *));
 
 extern int fat_flush_inodes(struct super_block *sb, struct inode *i1,
 		            struct inode *i2);