Use helm-map prefix instead of hard-coded binding

[NimoTh]

https://github.com/tuhdo/emacs-c-ide-demo/blob/5e77bb7caedd65ba420b8f6eb2d7ff799c38636a/custom/setup-helm.el#L79

In this and the following three lines, why not use the previously defined helm-map prefix? I think it makes sense to rebind these keys, as well, if the prefix is changed. Currently, they will always be bound to, e.g., "C-c h o" no matter how the prefix is bound.