How to make my Deo-nano work on 100Hz with internal clock?
You need hook up the posedge clk_50mhz to the internal oscillator of the FPGA device you are using. Normally the vendor will supply you will convenient tools that you can do this with and that will generate the appropriate code. 

In your case this could be for example be the tool "Quartus Prime Lite Edition" and the document "Quartus Prime Standard Edition Handbook Volume 1: Design and Synthesis" at chapter "Resource Property Editor" would probably help you.