BEN HARPER & THE INNOCENT CRIMINALS Live From Mars (Virgin) Rating: NNThere's no questioning the commitment of Ben Harper. And despite being a plainly average songwriter, the well-afroed Harper, with his firebrand intensity and flair for mysticism, has been elevated to the status of prophet by his fans. He spends most of his time on the road, so you'd think the double-disc set Live From Mars might help explain his fanatic appeal. Instead, it only helps to expose how hollow Harper's songwriting is. He's a great guitarist, shown best on the second acoustic disc, and he knows how to work a crowd into a sandal-flapping lather. When he and his Innocent Criminals band start into their sloppy blues boogie, though, it's closer to Phish than Harper would probably want to admit.