fix unknown types of riak_kv_mrc_pipe for dialyzer
fix unknown types of riak_kv_mrc_pipe for dialyzer

Unknown types:
  riak_kv_mrc_pipe:key_input/0
  riak_kv_mrc_pipe:link_match/0

(used in riak_kv_mrc_map)

andytill/riak_kv