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/affs/amigaffs.c b/fs/affs/amigaffs.c
index 3a4557e..8f12723 100644
--- a/fs/affs/amigaffs.c
+++ b/fs/affs/amigaffs.c
@@ -316,7 +316,7 @@
 	if (inode->i_nlink > 1)
 		retval = affs_remove_link(dentry);
 	else
-		inode->i_nlink = 0;
+		clear_nlink(inode);
 	affs_unlock_link(inode);
 	inode->i_ctime = CURRENT_TIME_SEC;
 	mark_inode_dirty(inode);