tools: depmod: fix -Walloc-size

tools: depmod: fix -Walloc-size

GCC 14 introduces a new -Walloc-size included in -Wextra which gives:
```
tools/depmod.c:192:14: warning: allocation of insufficient size ‘1’ for type ‘struct index_node’ with size ‘1048’ [-Walloc-size]
tools/depmod.c:255:11: warning: allocation of insufficient size ‘1’ for type ‘struct index_value’ with size ‘16’ [-Walloc-size]
tools/depmod.c:286:35: warning: allocation of insufficient size ‘1’ for type ‘struct index_node’ with size ‘1048’ [-Walloc-size]
tools/depmod.c:315:44: warning: allocation of insufficient size ‘1’ for type ‘struct index_node’ with size ‘1048’ [-Walloc-size]
```

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.

Signed-off-by: Sam James <sam@gentoo.org>