sh: Ensure all PG_dcache_dirty pages are written back.

With some of the cache rework an address aliasing optimization was added,
but this managed to fail on certain mappings resulting in pages with
PG_dcache_dirty set never writing back their dcache lines. This patch
reverts to the earlier behaviour of simply always writing back when the
dirty bit is set.
Signed-off-by: NMarkus Pietrek <Markus.Pietrek@emtrion.de>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/mm/cache.c

@@ -133,12 +133,8 @@ void __update_cache(struct vm_area_struct *vma,
 	page = pfn_to_page(pfn);
 	if (pfn_valid(pfn)) {
 		int dirty = test_and_clear_bit(PG_dcache_dirty, &page->flags);
-		if (dirty) {
-			unsigned long addr = (unsigned long)page_address(page);
-
-			if (pages_do_alias(addr, address & PAGE_MASK))
-				__flush_purge_region((void *)addr, PAGE_SIZE);
-		}
+		if (dirty)
+			__flush_purge_region(page_address(page), PAGE_SIZE);
 	}
 }