Fix type of loop variable in alloc_device().

[Vitaliy Margolen]

Gerald Pfeifer wrote:
> We iterate between 0 and and the value of an usigned variable, so we
> should adjust the loop variable accordingly (not the list to silence
> GCC).

> -    int i;
> +    unsigned i;

If there is nothing wrong about it, then why do you change it? If even gcc 
does not complain about it.

Vitaliy.