nilfs2: delete mark_inode_dirty from nilfs_set_link

Delete mark_inode_dirty() from nilfs_set_link() to reduce redundant
mark_inode_dirty() calls in caller of nilfs_set_link().

Signed-off-by: Jiro SEKIBA <jir@unicus.jp>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>