btrfs: convert btrfs_set_range_writeback() to use a folio

We already use a lot of functions here that use folios, update the
function to use __filemap_get_folio instead of find_get_page and then
use the folio directly.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -8958,19 +8958,19 @@ void btrfs_set_range_writeback(struct btrfs_inode *inode, u64 start, u64 end)
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
 	unsigned long index = start >> PAGE_SHIFT;
 	unsigned long end_index = end >> PAGE_SHIFT;
-	struct page *page;
+	struct folio *folio;
 	u32 len;
 
 	ASSERT(end + 1 - start <= U32_MAX);
 	len = end + 1 - start;
 	while (index <= end_index) {
-		page = find_get_page(inode->vfs_inode.i_mapping, index);
-		ASSERT(page); /* Pages should be in the extent_io_tree */
+		folio = __filemap_get_folio(inode->vfs_inode.i_mapping, index, 0, 0);
+		ASSERT(!IS_ERR(folio)); /* folios should be in the extent_io_tree */
 
 		/* This is for data, which doesn't yet support larger folio. */
-		ASSERT(folio_order(page_folio(page)) == 0);
-		btrfs_folio_set_writeback(fs_info, page_folio(page), start, len);
-		put_page(page);
+		ASSERT(folio_order(folio) == 0);
+		btrfs_folio_set_writeback(fs_info, folio, start, len);
+		folio_put(folio);
 		index++;
 	}
 }