sparc64: Fix D-cache flushing on swapin from SW devices.

Thanks to tip form ARM folks and Russell King.

If flush_dcache_page() occurs on a swapin it will have a mapping
and we'll try to defer the flush by setting the dirty bit.

But when it hits update_dcache_page() we won't flush because the
page won't have a mapping any more.  So remove the mapping
requirement in flush_dcache().
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/mm/init_64.c

@@ -265,7 +265,7 @@ static void flush_dcache(unsigned long pfn)
 	struct page *page;
 
 	page = pfn_to_page(pfn);
-	if (page && page_mapping(page)) {
+	if (page) {
 		unsigned long pg_flags;
 
 		pg_flags = page->flags;