Early as adverb means before the usual or expected time; earlier means before the present time or before the time one is referring to.
So, the second sentence could be understood as asking to come before the present time. For example, if it's 10:00 AM when the question is asked, the other person could take you are asking to come a little earlier than 10:00 AM.
The exact meaning depends on the context, though. For example, in the following sentence, the meaning would be different.
Yesterday we met at 10:00 PM. Can you come over earlier, so we can go back home before my wife returns from work?
I would use early if I am talking of the usual time I do something, or I am talking of the expected time something should happen. For example, if I am talking to a co-worker, I could ask Can you come early, tomorrow? to ask if my co-worker can come earlier than the usual time he starts to work.