After looking through the internet, I found out that I should have first called request_mem_region(). So I updated the code, ran it and found out request_mem_region fails which indicates that something else is already accessing those physical address.
As you suggest I refer the Topic 220249. I ran the following command
sudo devmem2 0x6000D004 w 0x10
And I got the following error
/dev/mem opened.
Memory mapped at address 0x7fb219400.
Bus error