xfs: use xfs_direct_write_iomap_ops for DAX zeroing

While the buffered write iomap ops do work due to the fact that zeroing
never allocates blocks, the DAX zeroing should use the direct ops just
like actual DAX I/O.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20211129102203.2243509-23-hch@lst.de
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Author: Christoph Hellwig

fs/xfs/xfs_iomap.c

@@ -1322,7 +1322,7 @@ xfs_zero_range(
 
 	if (IS_DAX(inode))
 		return dax_zero_range(inode, pos, len, did_zero,
-				      &xfs_buffered_write_iomap_ops);
+				      &xfs_direct_write_iomap_ops);
 	return iomap_zero_range(inode, pos, len, did_zero,
 				&xfs_buffered_write_iomap_ops);
 }
@@ -1337,7 +1337,7 @@ xfs_truncate_page(
 
 	if (IS_DAX(inode))
 		return dax_truncate_page(inode, pos, did_zero,
-					&xfs_buffered_write_iomap_ops);
+					&xfs_direct_write_iomap_ops);
 	return iomap_truncate_page(inode, pos, did_zero,
 				   &xfs_buffered_write_iomap_ops);
 }