ttm: Call shmem_writeout() from ttm_backup_backup_page()

The ->writepage operation is being removed.  Since this function
exclusively deals with shmem folios, we can call shmem_writeout()
to write it.

Signed-off-by: "Matthew Wilcox (Oracle)" <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: Matthew Wilcox (Oracle)

drivers/gpu/drm/ttm/ttm_backup.c

@@ -136,13 +136,13 @@ ttm_backup_backup_page(struct ttm_backup *backup, struct page *page,
 			.for_reclaim = 1,
 		};
 		folio_set_reclaim(to_folio);
-		ret = mapping->a_ops->writepage(folio_file_page(to_folio, idx), &wbc);
+		ret = shmem_writeout(to_folio, &wbc);
 		if (!folio_test_writeback(to_folio))
 			folio_clear_reclaim(to_folio);
 		/*
-		 * If writepage succeeds, it unlocks the folio.
-		 * writepage() errors are otherwise dropped, since writepage()
-		 * is only best effort here.
+		 * If writeout succeeds, it unlocks the folio.	errors
+		 * are otherwise dropped, since writeout is only best
+		 * effort here.
 		 */
 		if (ret)
 			folio_unlock(to_folio);