device/dram/ddr4.c: note that dimm size calculation won't work for 3DS

Change-Id: I52548e544165b4732d9989da6455c8fd77bf99d3
Signed-off-by: Krystian Hebel <krystian.hebel@3mdeb.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67185
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>

src/device/dram/ddr4.c

@@ -248,6 +248,7 @@ int spd_decode_ddr4(struct dimm_attr_ddr4_st *dimm, spd_raw_data spd)
 	dimm->vdd_voltage = 1200;
 
 	/* calculate size */
+	/* FIXME: this is wrong for 3DS devices */
 	dimm->size_mb = cap_per_die_mbit / 8 * bus_width / sdram_width * dimm->ranks;
 
 	dimm->ecc_extension = spd[SPD_PRIMARY_SDRAM_WIDTH] & SPD_ECC_8BIT;