mm/mapping_dirty_helpers: enhance the kernel-doc markups

mm/mapping_dirty_helpers: enhance the kernel-doc markups

Add and change parameter explanation for wp_pte and clean_record_pte, to
avoid W1 warning:

  mm/mapping_dirty_helpers.c:34: warning: Function parameter or member 'end' not described in 'wp_pte'
  mm/mapping_dirty_helpers.c:88: warning: Function parameter or member 'end' not described in 'clean_record_pte'

Link: https://lkml.kernel.org/r/1605605088-30668-2-git-send-email-alex.shi@linux.alibaba.com
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>