examples: Avoid one extra barrier in parallel reduction example
examples: Avoid one extra barrier in parallel reduction example

For Mesa's i965 driver, this might only work correctly for recent
versions (Mesa >= 18.2.x).

Signed-off-by: onox <34c1d3d2d1347bea60a26f46574de21a7a79b6d5@gmail.com>

onox/orka