mtd: nand: sunxi: rely on nand_dt_init initialization

nand_dt_init(), called from nand_scan_ident(), is already parsing the
generic MTD/NAND DT properties, and initializing the nand_chip struct
accordingly.
Rely on this initialization instead of manually parsing those properties.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
[Brian: rename 'np' -> 'flash_node' to accomodate for prior rename patch]
Signed-off-by: Brian Norris <computersforpeace@gmail.com>