mtd: nand: sunxi: make use of sunxi_nfc_hw_ecc_read/write_chunk()

The sunxi_nfc_hw_ecc_read/write_chunk() functions have been created to
factorize the code in the normal and syndrome ECC implementation.
Make use of them where appropriate.

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