nilfs2: do not acquire rwsem in nilfs_bmap_write()

nilfs2: do not acquire rwsem in nilfs_bmap_write()

It is now clear that nilfs_bmap_write() is only used to finalize logs
written to disk.  Concurrent bmap modification operations are not
performed on bmaps in this context.  Additionally, this function does not
modify data used in read-only operations such as bmap lookups.

Therefore, there is no need to acquire bmap->b_sem in nilfs_bmap_write(),
so delete it.

Link: https://lkml.kernel.org/r/20240122140202.6950-10-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>