nilfs2: convert nilfs_make_empty() to use a folio

Remove two calls to compound_head() and switch from kmap_atomic to
kmap_local.

Link: https://lkml.kernel.org/r/20231127143036.2425-16-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>