drivers/net/wan/z85230.c: Use designated initializers

In preparation for the randstruct gcc plugin performing randomization of
structures that are entirely function pointers, use designated initializers
so the compiler doesn't get angry.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: David S. Miller <davem@davemloft.net>