mtd: spinand: fix memory leak of ECC engine conf

Memory allocated for the ECC engine conf is not released during spinand
cleanup. Below kmemleak trace is seen for this memory leak:

unreferenced object 0xffffff80064f00e0 (size 8):
  comm "swapper/0", pid 1, jiffies 4294937458
  hex dump (first 8 bytes):
    00 00 00 00 00 00 00 00                          ........
  backtrace (crc 0):
    kmemleak_alloc+0x30/0x40
    __kmalloc_cache_noprof+0x208/0x3c0
    spinand_ondie_ecc_init_ctx+0x114/0x200
    nand_ecc_init_ctx+0x70/0xa8
    nanddev_ecc_engine_init+0xec/0x27c
    spinand_probe+0xa2c/0x1620
    spi_mem_probe+0x130/0x21c
    spi_probe+0xf0/0x170
    really_probe+0x17c/0x6e8
    __driver_probe_device+0x17c/0x21c
    driver_probe_device+0x58/0x180
    __device_attach_driver+0x15c/0x1f8
    bus_for_each_drv+0xec/0x150
    __device_attach+0x188/0x24c
    device_initial_probe+0x10/0x20
    bus_probe_device+0x11c/0x160

Fix the leak by calling nanddev_ecc_engine_cleanup() inside
spinand_cleanup().

Signed-off-by: Pablo Martin-Gomez <pmartin-gomez@freebox.fr>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>