net/handshake: Fix uninitialized local variable

trace_handshake_cmd_done_err() simply records the pointer in @req,
so initializing it to NULL is sufficient and safe.

Reported-by: Dan Carpenter <[e-mail]>
Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests")
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

net/handshake/netlink.c

···
 int handshake_nl_done_doit(struct sk_buff *skb, struct genl_info *info)
 {
 	struct net *net = sock_net(skb->sk);
+	struct handshake_req *req = NULL;
 	struct socket *sock = NULL;
-	struct handshake_req *req;
 	int fd, status, err;
 
 	if (GENL_REQ_ATTR_CHECK(info, HANDSHAKE_A_DONE_SOCKFD))