nb/sandybridge: Remove redundant include of "ddr3.c"

It is already selected here device/dram/Makefile.inc

Change-Id: I32a1ecc4e0f90725f9356158ce2978502b590d5c
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76390
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/northbridge/intel/sandybridge/Makefile.inc

@@ -25,7 +25,6 @@ romstage-y += raminit_common.c
 romstage-y += raminit_iosav.c
 romstage-y += raminit_native.c
 romstage-y += raminit_tables.c
-romstage-y += ../../../device/dram/ddr3.c
 else
 romstage-y += raminit_mrc.c
 cbfs-files-y += mrc.bin