Afair u-boot had (has?) the stock kernel attached.
So you should have only selected run attached kernel!?

Now you have cssu kernel and possibly no modules, as said. I would go and flash the u-boot kernel (package u-boot-flasher) if its size is around 2MB. Then you should be able to run attached kernel.
Furthermore ther is u-boot console giving you the possibility to "run noloboot" which should also work. More info in u-boot thread.

If all fails, just extract stock kernel and load/flash this one to device, as you have done with cssu. This should boot.