[MTD] [NAND] fix possible Ooops in rfc_from4

I found this while I was looking how the rs_lib is working.  The rs_decoder is
initialized _after_ the nand core code read the BBT table and _after_ the
partition table has been added.  The driver has a private BBT description
which is in located in flash data so we Ooops if there is a bit flip _or_ if a
bit flips while reading the partition table.

This patch moves the initialization of the rs_lib before the first possible
access by nand core.

Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jörn Engel <joern@wh.fh-wedel.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>