mb/getac/p470: Null-terminate ec_id string buffer

The EC ID of the ECDT needs to be null-terminated (see ACPI specification,
section 5.2.15), which currently isn't being done due to an off-by-one
error. strncpy() is bug-prone exactly because of issues like this, so just
skip it entirely and use memcpy() instead.

Change-Id: I0b62e1f32177c9768fa978053ab26bca93d7248d
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Found-by: Coverity CID 1402104
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34374
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/mainboard/getac/p470/acpi_tables.c

@@ -70,7 +70,7 @@ static long acpi_create_ecdt(acpi_ecdt_t * ecdt)
 
 	ecdt->gpe_bit = 23; // SCI interrupt within GPEx_STS
 
-	strncpy((char *)ecdt->ec_id, ec_id, strlen(ec_id));
+	memcpy(ecdt->ec_id, ec_id, sizeof(ec_id));
 
 	header->checksum =
 	    acpi_checksum((void *) ecdt, ecdt_len);