src: include <assert.h> when appropriate

Change-Id: Ib843eb7144b7dc2932931b9e8f3f1d816bcc1e1a
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/26796
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: David Guckian

src/superio/smsc/lpc47n227/early_serial.c

@@ -17,7 +17,9 @@
 /* Pre-RAM driver for SMSC LPC47N227 Super I/O chip. */
 
 #include <arch/io.h>
+#include <assert.h>
 #include <device/pnp_ops.h>
+
 #include "lpc47n227.h"
 
 void pnp_enter_conf_state(pnp_devfn_t dev)