filesystems: add missing nlink wrappers

Replace direct i_nlink updates with the respective updater function
(inc_nlink, drop_nlink, clear_nlink, inode_dec_link_count).

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 666628b..08ac272 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -354,7 +354,7 @@
 
  failed_acl:
  failed_bmap:
-	inode->i_nlink = 0;
+	clear_nlink(inode);
 	iput(inode);  /* raw_inode will be deleted through
 			 generic_delete_inode() */
 	goto failed;