If you flashed TP-Link's firmware image as is, you've got a soft-brick now. Their firmware image uses a custom format, and cannot be written directly to flash (which is what sysupgrade does). You would need to build tplink-safeloader from the OpenWrt sources to convert a TP-Link firmware file into a valid OpenWrt firmware file.
I'm not entirely sure anymore, but I think this device will launch a failsafe web server at the default address (192.168.1.1) if it fails to boot. This failsafe page should accept TP-Link images.