pagewalk: prefix struct kernel-doc descriptions

The script './scripts/kernel-doc -none ./include/linux/pagewalk.h' reports:

  include/linux/pagewalk.h:37: warning: cannot understand function prototype: 'struct mm_walk_ops '
  include/linux/pagewalk.h:85: warning: cannot understand function prototype: 'struct mm_walk '

A kernel-doc description for a structure requires to prefix the struct
name with the keyword 'struct'.  So, do that such that no further
kernel-doc warnings are reported for this file.

Link: https://lkml.kernel.org/r/20210322122542.15072-3-lukas.bulwahn@gmail.comSigned-off-by: NLukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ralf Ramsauer <ralf.ramsauer@oth-regensburg.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/pagewalk.h

@@ -7,7 +7,7 @@
 struct mm_walk;
 
 /**
- * mm_walk_ops - callbacks for walk_page_range
+ * struct mm_walk_ops - callbacks for walk_page_range
  * @pgd_entry:		if set, called for each non-empty PGD (top-level) entry
  * @p4d_entry:		if set, called for each non-empty P4D entry
  * @pud_entry:		if set, called for each non-empty PUD entry
@@ -71,7 +71,7 @@ enum page_walk_action {
 };
 
 /**
- * mm_walk - walk_page_range data
+ * struct mm_walk - walk_page_range data
  * @ops:	operation to call during the walk
  * @mm:		mm_struct representing the target process of page table walk
  * @pgd:	pointer to PGD; only valid with no_vma (otherwise set to NULL)