device/i2c_bus: Constify i2c_busdev and i2c_link

Change-Id: If795087ecdaea24ad7834dcc6d5bf6a72f2aea8f
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63208
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/device/i2c_bus.c

@@ -6,7 +6,7 @@
 #include <device/i2c_bus.h>
 #include <commonlib/endian.h>
 
-struct bus *i2c_link(struct device *const dev)
+struct bus *i2c_link(const struct device *const dev)
 {
 	if (!dev || !dev->bus)
 		return NULL;