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/ubifs/xattr.c b/fs/ubifs/xattr.c
index 16f19f5..993adc8 100644
--- a/fs/ubifs/xattr.c
+++ b/fs/ubifs/xattr.c
@@ -558,7 +558,7 @@
 	}
 
 	ubifs_assert(inode->i_nlink == 1);
-	inode->i_nlink = 0;
+	clear_nlink(inode);
 	err = remove_xattr(c, host, inode, &nm);
 	if (err)
 		inode->i_nlink = 1;