Ignore all warnings in generated riak_core_pb

Because tools.mk performs a simple grep filter using the patterns in
dialyzer.ignore-warnings, simply using the module name (with the extra
colon just to be a bit safer) is enough to make it ignore all warnings
in that module. This should be a time saver

/cc @reiddraper   I'm preparing a separate tools.mk PR to deal with the line number issue.