nand: atmel: Initialize pmecc smu with correct size

nand: atmel: Initialize pmecc smu with correct size

Currently in pmecc_get_sigma(), the code tries to clear the memory
pointed by smu with wrong size 'sizeof(int16_t) * ARRAY_SIZE(smu)'.
Since smu is actually a pointer, not an array, so ARRAY_SIZE(smu)
does not generate correct size to be cleared.

In fact, GCC 8.1.0 reports a warning against it:

error: division 'sizeof (int16_t * {aka short int *}) / sizeof (int16_t
{aka short int})' does not compute the number of array elements
[-Werror=sizeof-pointer-div]

Fix it by using the correct size.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>