[JFFS2] Rename function and update comments

We recently changed the method of collecting and sorting of
tmp_dnode objects to use a temporary RB-tree instead of a
temporary list. Rename function and update comments.

Signed-off-by: Artem B. Bityuckiy <dedekind@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>