nilfs2: convert nilfs_empty_dir() to use a folio

Remove three calls to compound_head() by using the folio API.

Link: https://lkml.kernel.org/r/20231127143036.2425-15-konishi.ryusuke@gmail.com


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>