mtd: rawnand: nuvoton: Fix an error handling path in ma35_nand_chips_init()

If a ma35_nand_chip_init() call fails, then a reference to 'nand_np' still
needs to be released.

Use for_each_child_of_node_scoped() to fix the issue.

Fixes: 5abb5d41 ("mtd: rawnand: nuvoton: add new driver for the Nuvoton MA35 SoC")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>