src: Remove unused 'include <stddef.h>

Change-Id: Iae1e875b466f8a195653d897efa1b297c61ad0a5
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41912
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/riscv/arch_timer.c

@@ -3,7 +3,6 @@
 #include <device/mmio.h>
 #include <arch/encoding.h>
 #include <console/console.h>
-#include <stddef.h>
 #include <timer.h>
 #include <mcall.h>
 

src/arch/riscv/misaligned.c

@@ -1,6 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
-#include <stddef.h>
 #include <stdint.h>
 #include <vm.h>
 #include <arch/exception.h>

src/arch/riscv/smp.c

@@ -1,6 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
-#include <stddef.h>
 #include <arch/encoding.h>
 #include <arch/smp/smp.h>
 #include <arch/smp/spinlock.h>