If Africa's land can't feed the people there, for some intrinsical reason, then feeding people in Africa is unsustainable, and we'd better move them elsewhere.
If Africa's land is capable of feeding the people there, then the real question is: Why can't it today? Are we going for the cause, or for the symptom?
It could be that by eliminating hunger temporarily we'd start a virtuous cycle of some kind, but it'd be a totally random side-effect.
In the grand scheme of things, feeding people for hunger-squashing sake, while noble and charitable and christian-good, amounts to very little. Colonizing Mars is the first guarantee that humans don't go the way of the Dodo in a Great Dying event[1]. Earth had five of those, and we still have to prove ourselves less stupid than dinosaurs.
[1] http://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinc...
The people who say stuff like this are always far, far away from the experience of not having anything to eat. It could be true that Musk's projects in the long run could have do more good for humanity in the long run, but also in a different sense. How is colonizing Mars, or having electric cars does more good for a whole continent that hasn't solved dozens of problems well below any technological/energetic one? What I'm saying is, it might do more good for the developed world, but not for Africa. Bill Gates was right when he criticized Google's balloon internet project. What the african population really needs is different. To say otherwise is to be too removed from the real, basic, almost elementary problems that are still present in the continent.
(edit: I meant no offense to the parent with my first sentence. But I've been to Africa, and I live in a 3rd world country with some very, very poor regions. Space programs have very little effect on life there.)