nb/intel/haswell: Constify pointers to strings

Jenkins complains about it.

Change-Id: I20abdd01ca2b93e8a4de31664ff48651e7268d25
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46368
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/northbridge/intel/haswell/raminit.c

@@ -51,7 +51,7 @@ static void prepare_mrc_cache(struct pei_data *pei_data)
 	       pei_data->mrc_input, mrc_size);
 }
 
-static const char *ecc_decoder[] = {
+static const char *const ecc_decoder[] = {
 	"inactive",
 	"active on IO",
 	"disabled on IO",