nilfs2: convert nilfs_prepare_chunk() and nilfs_commit_chunk() to folios

All callers now have a folio, so convert these two functions.
Saves one call to compound_head() in unlock_page().

[konishi.ryusuke: resolved conflicts in nilfs_{set_link,delete_entry}]
Link: https://lkml.kernel.org/r/20231127143036.2425-17-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>