mtd: rawnand: nandsim: Fix the logic when selecting Hamming soft ECC engine

I have been fooled by the logic picking the right ECC engine which is
spread across two functions: *init_module() and *_attach(). I thought
this driver was not impacted by the recent changes around the ECC
engines DT parsing logic but in fact it is.

Reported-by: kernel test robot <oliver.sang@intel.com>
Fixes: d7157ff4 ("mtd: rawnand: Use the ECC framework user input parsing bits")
Cc: stable@vger.kernel.org
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210104093057.31178-1-miquel.raynal@bootlin.com