hfsplus: remove ->writepage

->writepage is a very inefficient method to write back data, and only
used through write_cache_pages or a a fallback when no ->migrate_folio
method is present.

Set ->migrate_folio to the generic buffer_head based helper, and stop
wiring up ->writepage for hfsplus_aops.

Link: https://lkml.kernel.org/r/20221202102644.770505-5-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/hfsplus/inode.c

@@ -170,12 +170,12 @@ const struct address_space_operations hfsplus_aops = {
 	.dirty_folio	= block_dirty_folio,
 	.invalidate_folio = block_invalidate_folio,
 	.read_folio	= hfsplus_read_folio,
-	.writepage	= hfsplus_writepage,
 	.write_begin	= hfsplus_write_begin,
 	.write_end	= generic_write_end,
 	.bmap		= hfsplus_bmap,
 	.direct_IO	= hfsplus_direct_IO,
 	.writepages	= hfsplus_writepages,
+	.migrate_folio	= buffer_migrate_folio,
 };
 
 const struct dentry_operations hfsplus_dentry_operations = {