treewide: Add missing include guards to chip.h

Some of the chip.h files in the tree are missing the include guards.

This patch adds them in order to avoid potential redefinions of symbols
contained in these headers, when they are included multiple times in
static.c generated by sconfig.

Change-Id: I550a514e72a8dd4db602e7ceffccd81aa36446e3
Signed-off-by: Jan Samek <jan.samek@siemens.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74749
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
diff --git a/src/drivers/i2c/ptn3460/chip.h b/src/drivers/i2c/ptn3460/chip.h
index 2bf7e5e..0ec26ca 100644
--- a/src/drivers/i2c/ptn3460/chip.h
+++ b/src/drivers/i2c/ptn3460/chip.h
@@ -1,5 +1,10 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#ifndef __DRIVERS_I2C_PTN3460_CHIP_H__
+#define __DRIVERS_I2C_PTN3460_CHIP_H__
+
 struct drivers_i2c_ptn3460_config {
 
 };
+
+#endif /* __DRIVERS_I2C_PTN3460_CHIP_H__ */