vfs: make first argument of dir_context.actor typed

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/fs.h

@@ -1467,7 +1467,10 @@ int fiemap_check_flags(struct fiemap_extent_info *fieinfo, u32 fs_flags);
  * This allows the kernel to read directories into kernel space or
  * to have different dirent layouts depending on the binary type.
  */
-typedef int (*filldir_t)(void *, const char *, int, loff_t, u64, unsigned);
+struct dir_context;
+typedef int (*filldir_t)(struct dir_context *, const char *, int, loff_t, u64,
+			 unsigned);
+
 struct dir_context {
 	const filldir_t actor;
 	loff_t pos;