container_of: Update header inclusions

The commit 848dba781f19 ("container_of: remove container_of_safe()")
removed the code that uses err.h. Replace the inclusion by stddef.h
which provides offsetof() definition which is still in use.

Signed-off-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/linux/container_of.h

···
 #define _LINUX_CONTAINER_OF_H
 
 #include <linux/build_bug.h>
-#include <linux/err.h>
+#include <linux/stddef.h>
 
 #define typeof_member(T, m)	typeof(((T*)0)->m)