[JFFS2] Fix NOR specific scan BUG

Fix fairly sad NOR-specific bug - during FS building ic->scan_dents
isn't zero, but jffs2_mark_node_obsolete() migt be called it tries to
finde the ic corresponding to ref - this requires ic->scan_dents = 0.

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