mb/intel/harcuvar: Fix strict prototype warning

Clang warns on both the declaration and the definction.

Change-Id: I94d979fcdbe41349c59248656066615bffd215b6
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69308
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/mainboard/intel/harcuvar/spd/spd.c

@@ -6,7 +6,7 @@
 #include "spd.h"
 
 /* Get SPD data for on-board memory */
-uint8_t *mainboard_find_spd_data()
+uint8_t *mainboard_find_spd_data(void)
 {
 	uint8_t *spd_data;
 	int spd_index;