nilfs2: convert nilfs_copy_buffer() to use kmap_local

The routine nilfs_copy_buffer() that copies a block buffer still uses the
deprecated kmap_atomic(), so convert it to use kmap_local.

Link: https://lkml.kernel.org/r/20240122140202.6950-4-konishi.ryusuke@gmail.com


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