*.h: Fix up typos in guarding

Clang complains about this.

Change-Id: I421d6c5daa373d1537e4ac2243438e7f1f6208d1
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63067
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/riscv/include/arch/barrier.h

@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: BSD-3-Clause */
 
-#ifndef __ARCH_BARRIER_H_
+#ifndef __ARCH_BARRIER_H__
 #define __ARCH_BARRIER_H__
 
 static inline void mb(void)  { asm volatile("fence"); }