more file_inode() open-coded instances

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/kernel/futex.c b/kernel/futex.c
index fbc07a2..f0090a9 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -226,7 +226,7 @@
  * Returns a negative error code or 0
  * The key words are stored in *key on success.
  *
- * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
+ * For shared mappings, it's (page->index, file_inode(vma->vm_file),
  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
  * We can usually work out the index without swapping in the page.
  *