nilfs2: convert metadata file common code to use kmap_local

In the common code of metadata files, the new block creation routine
nilfs_mdt_insert_new_block() still uses the deprecated kmap_atomic(), so
convert it to use kmap_local.

Link: https://lkml.kernel.org/r/20240122140202.6950-5-konishi.ryusuke@gmail.com


Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>