How to read values from a ROM to control a VGA monitor
Been unanswered for a day so let me give it a shot.
That ROM is very unusual. I have been an ASIC engineer for more then 25 years and I have never seen a ROM (or memory) with one port and two clocks. 
Try to find the model for that ROM or find the specs if it is a FPGA library element. Failing that my best guess would be to use the same clock for both ports. You say you are working on VGA which requires 25 MHz so that is probably your pixel clock. Then you must output three analog signals every clock cycle. (And hsync, vsync + pixel clock). Your 24 bit wide ROM is probably RGB as 888 thus you must clock that ROM out at 25 MHz. 
Alternative you could try to use an opposite clock for address and data.