IB/mlx4: Fix error paths in mlx4_ib_create_flow()

The unwinding clean up code are err_create_flow starts at the current
index i.  That means we shouldn't increment i until we're really sure
we won't have to destroy the current flow; otherwise we might
increment the index, fail inside an is_bonded block, and end up
accessing off the end of the reg_id[] array.

This was detected by Coverity (CID 1271229).

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>