console-server: add ifdef around offsetof

GCC 12.2 seems to supply offsetof inside `stddef.h`.  Add guards
around the define here so that we do not end up with the following
compiler warnings:

```
22:35:49 | ../git/console-server.h:153: error: "offsetof" redefined [-Werror]
```

Change-Id: Id8d940db441a7ee96caf0a9a66e1ef3863cd3d2e
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/console-server.h b/console-server.h
index b6ab1b8..9386b4e 100644
--- a/console-server.h
+++ b/console-server.h
@@ -150,8 +150,10 @@
 
 #define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
 
+#ifndef offsetof
 #define offsetof(type, member) \
 	((unsigned long)&((type *)NULL)->member)
+#endif
 
 #define container_of(ptr, type, member) \
 	((type *)((void *)((ptr) - offsetof(type, member))))