bus: skip useless iterations in find function

bus: skip useless iterations in find function

The starting point is known. The iterator can be directly set to it.

The function rte_bus_find can easily be used with a comparison function
always returning True. This would make it a regular bus iterator.

Users doing so would however accomplish such iteration in

   O(N * N/2) = O(N^2)

Which can be avoided.

Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>