configs: sama5d2_ptc_ek: fix NAND PMECC_CAP

configs: sama5d2_ptc_ek: fix NAND PMECC_CAP

CONFIG_PMECC_CAP has a higher priority than its ONFI detected
parameter and will overwrite it when defined. As per commit
49ad40298cc5, CONFIG_PMECC_CAP has a default value of 2 if not
otherwise stated. This results in the overwriting of the ONFI ECC
bits value. The following errors are seen when booting the kernel
from the nand flash:

Loading Environment from NAND... PMECC: Too many errors
NAND read from offset 140000 failed -74
*** Warning - some problems detected reading environment; recovered successfully
*** Warning - bad CRC, using default environment

In:    serial
Out:   serial
Err:   serial
Net:   eth0: ethernet@f8008000
Hit any key to stop autoboot:  0

NAND read: device 0 offset 0x180000, size 0x80000
PMECC: Too many errors
NAND read from offset 180000 failed -74
 0 bytes read: ERROR

NAND read: device 0 offset 0x200000, size 0x600000
PMECC: Too many errors
NAND read from offset 200000 failed -74
 0 bytes read: ERROR
Bad Linux ARM zImage magic!

Fix it by setting the right value for ECC bits.

Fixes: 49ad40298cc5 ("ARM: at91: Convert SPL_GENERATE_ATMEL_PMECC_HEADER to Kconfig")
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>