mm: rmap: use the correct parameter name for DEFINE_PAGE_VMA_WALK

The parameter used by DEFINE_PAGE_VMA_WALK is _page not page, fix the
parameter name.  It didn't cause any build error, it is probably because
the only caller is write_protect_page() from ksm.c, which pass in page.

Link: https://lkml.kernel.org/r/20220512174551.81279-1-shy828301@gmail.com
Fixes: 2aff7a47 ("mm: Convert page_vma_mapped_walk to work on PFNs")
Signed-off-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/rmap.h

@@ -325,8 +325,8 @@ struct page_vma_mapped_walk {
 #define DEFINE_PAGE_VMA_WALK(name, _page, _vma, _address, _flags)	\
 	struct page_vma_mapped_walk name = {				\
 		.pfn = page_to_pfn(_page),				\
-		.nr_pages = compound_nr(page),				\
-		.pgoff = page_to_pgoff(page),				\
+		.nr_pages = compound_nr(_page),				\
+		.pgoff = page_to_pgoff(_page),				\
 		.vma = _vma,						\
 		.address = _address,					\
 		.flags = _flags,					\