Update repair count type specs in riak_kv_entropy_info

Change the repaired field of the exchange_info record in the 
riak_kv_entropy_info module from a type of pos_integer() to non_neg_integer().
Also change the Repaired parameter type for 
riak_kv_entropy_info:exchange_complete/4 and 
riak_kv_entropy_info:exchange_complete/5 to be non_neg_integer().