If you're liking the idea of some code and some controls, you can get a good foundation in both with a Computer Engineering degree. That would give you the flexibility to focus on different aspects of computing/controls systems (or one, if you find you really like a particular area) and is a perfect companion to ME. If you go all software (Computer Science), you miss out on the understanding of how the electrics/electronics work and if you go all hardware (Electrical Engineering), you miss out on the higher level integration aspects of what modern software environments can really do. Also, just being able to speak the language of MEs, EEs, and CSCs is invaluable when working in multi/inter-disciplinary scenarios.
Full disclosure: I am a Computer Engineer specializing in (semi)autonomous robotics systems (and /love/ it).