Ridge Racer hack: Flush after every prim if fb addr == tex addr.

Fixes the bloom errors. @unknownbrackets discovered this method.

Not sure if I want to merge this.. It does add yet another check
to a critical path.
Merge pull request #6396 from hrydgard/ridge-racer-hack

Ridge Racer hack: Flush after every prim if fb addr == tex addr.