[CRYPTO] api: Flush the current page right than the next

On platforms where flush_dcache_page is needed we're currently flushing
the next page right than the one we've just processed.  This patch fixes
the off-by-one error.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/scatterwalk.c b/crypto/scatterwalk.c
index 0f76175..81afd17 100644
--- a/crypto/scatterwalk.c
+++ b/crypto/scatterwalk.c
@@ -59,8 +59,12 @@
 static void scatterwalk_pagedone(struct scatter_walk *walk, int out,
 				 unsigned int more)
 {
-	if (out)
-		flush_dcache_page(scatterwalk_page(walk));
+	if (out) {
+		struct page *page;
+
+		page = walk->sg->page + ((walk->offset - 1) >> PAGE_SHIFT);
+		flush_dcache_page(page);
+	}
 
 	if (more) {
 		walk->offset += PAGE_SIZE - 1;