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/southbridge/intel/lynxpoint/pcie.c

@@ -12,7 +12,6 @@
 #include "iobp.h"
 #include "pch.h"
 #include <southbridge/intel/common/gpio.h>
-#include <stddef.h>
 #include <stdint.h>
 #include "chip.h"