mtd: rawnand: nandsim: Free erase_block_wear on error

Free erase_block_wear on error, which is allocated by
ns_setup_wear_reporting().

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200525085851.17682-14-miquel.raynal@bootlin.com