src/drivers/usb/ehci_debug.c: Add missing include

Replace unused <stddef.h> with missing <stdint.h>. This is needed for 'u64'.

Change-Id: Ie99c27bd6a7d982bba9a93342f3e3b83a1c09e8d
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43341
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/drivers/usb/ehci_debug.c

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