x86: Fix i8254 ifdef include guard

x86: Fix i8254 ifdef include guard

When building U-Boot with clang, it notices that the i8254.h include
guard does not work correctly due to a typo. Fix it.

Signed-off-by: Alistair Delva <adelva@google.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
[bmeng: fixed the other same typo at the end of the same file]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>