Some fixes to autoadmin_cache_function()

I found cache_get($cache) is wrong and did also other fixes in this function.

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I wonder what's the intention for this function. It is only used to cache the result of autoadmin_schema_get_all() and $options argument is only used to clear the cache. If it is planned to support caching the result of other functions I suggest this signature:

function autoadmin_cache_function($function, $arguments = array(), $reset = FALSE)).. and also use call_user_func_array() instead.