ksmbd: switch to use kmemdup_nul() helper

Use kmemdup_nul() helper instead of open-coding to
simplify the code.
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/server/asn1.c

@@ -214,12 +214,10 @@ static int ksmbd_neg_token_alloc(void *context, size_t hdrlen,
 {
 	struct ksmbd_conn *conn = context;
 
-	conn->mechToken = kmalloc(vlen + 1, GFP_KERNEL);
+	conn->mechToken = kmemdup_nul(value, vlen, GFP_KERNEL);
 	if (!conn->mechToken)
 		return -ENOMEM;
 
-	memcpy(conn->mechToken, value, vlen);
-	conn->mechToken[vlen] = '\0';
 	return 0;
 }