Before fixing the problem, consider the cause of the pitting. Typically, this is caused by either rock salt or road salt. The salts can serrate concrete rather quickly, so as a matter of practice you should switch to calcium chloride pellets for melting snow - not sodium-based rock salt, which is corrosive.
In terms of repair, try Quickrete Concrete Patching Compound. And no matter what your solution, avoid the most common mistake when repairing concrete, which is putting new concrete on top of old, damaged concrete. It doesn't work. The old concrete doesn't have the necessary adhesive qualities, and as soon as the patched job gets wet or freezes, that new layer comes right off.