mtd: rawnand: jz4740: fix probe function error path

An error after nand_scan_tail() should trigger a nand_cleanup(), not a
nand_release() as mtd_device_register() (or one of its variants) has not
been called and there is no need to deregister any MTD device yet.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>