src/device: Fix discarded-qualifiers compilation issue

coreboot build is broken due to
CL: I6830a65bc9cea2907f4209bb97a53ccebcbf248d

This patch ensures to build coreboot successfully.

Change-Id: I4c9dfc9b19ce159ce1abcfbb287be4ce273cbaf1
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/25985
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/console/post.c

@@ -108,7 +108,7 @@ void post_log_extra(u32 value)
 	spin_unlock(&cmos_post_lock);
 }
 
-void post_log_path(struct device *dev)
+void post_log_path(const struct device *dev)
 {
 	if (dev) {
 		/* Encode path into lower 3 bytes */