mb/asrock/h110m/Makefile.mk: Remove superfluous spd from subdirs-y

The H110M does not use memory down, and the spd directory doesn't exist
in the board's directory in the first place. This was probably just copy
and paste leftover from some existing Skylake board in the initial port.

TEST=Timeless build does not change.

Change-Id: I35744310b2bf8a14165dae9808c982e6dc274a74
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83010
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/asrock/h110m/Makefile.mk

@@ -1,6 +1,5 @@
 ## SPDX-License-Identifier: GPL-2.0-only
 
-subdirs-y += spd
 bootblock-y += bootblock.c
 
 ramstage-y += mainboard.c