soc/intel/common/block/memory: Always write `data->spd_len`

The `data->spd_len` option always needs to be initialised. However, it
did not get set when using a mixed memory topology. Correct this bug.

Fixes: commit 859ca18ced
Change-Id: I8a165f000e5d52e49de18d7648d02fe76d2dd296
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50786
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-by: EricR Lai <ericr_lai@compal.corp-partner.google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/common/block/memory/meminit.c

@@ -167,5 +167,7 @@ void mem_populate_channel_data(const struct soc_mem_cfg *soc_mem_cfg,
 		 */
 		if (spd_md_len != spd_dimm_len)
 			die("Length of SPD does not match for mixed topology!\n");
+
+		data->spd_len = spd_md_len;
 	}
 }