mtd: nand: sunxi: fix call order in sunxi_nand_chip_init()

sunxi_nand_chip_set_timings() is extracting a pointer to the nfc from the
nand->controller field, but this field is initialized after
sunxi_nand_chip_set_timings() call.
Reorder the calls to avoid any problem.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>