misc: fix -Walloc-size warnings

GCC 14 introduces a new -Walloc-size included in -Wextra which gives:

```
src/tool_operate.c: In function ‘add_per_transfer’:
src/tool_operate.c:213:5: warning: allocation of insufficient size ‘1’ for type ‘struct per_transfer’ with size ‘480’ [-Walloc-size]
  213 |   p = calloc(sizeof(struct per_transfer), 1);
      |     ^
src/var.c: In function ‘addvariable’:
src/var.c:361:5: warning: allocation of insufficient size ‘1’ for type ‘struct var’ with size ‘32’ [-Walloc-size]
  361 |   p = calloc(sizeof(struct var), 1);
      |     ^
```

The calloc prototype is:
```
void *calloc(size_t nmemb, size_t size);
    ```

So, just swap the number of members and size arguments to match the
prototype, as we're initialising 1 struct of size `sizeof(struct
...)`. GCC then sees we're not doing anything wrong.

Closes #12292

lib/cf-https-connect.c

@@ -455,7 +455,7 @@ static CURLcode cf_hc_create(struct Curl_cfilter **pcf,
   CURLcode result = CURLE_OK;
 
   (void)data;
-  ctx = calloc(sizeof(*ctx), 1);
+  ctx = calloc(1, sizeof(*ctx));
   if(!ctx) {
     result = CURLE_OUT_OF_MEMORY;
     goto out;