The ornamental design for a surfaceconfiguration of a diffuser for a bumper of a vehicle, as shown and described.
FIG. 1 is a right perspective view of a surface configuration of a diffuser for a bumper of a vehicle according to my novel design;
FIG. 2 is a front view of the surface configuration of a diffuser for a bumper of a vehicle according to my novel design;
FIG. 3 is a left side view of the surface configuration of a diffuser for a bumper of a vehicle according to my novel design; and,
FIG. 4 is a left perspective view of the surface configuration of a diffuser for a bumper of a vehicle according to my novel design, showing the placement on the bumper.
The broken lines are for illustrative purposes only and form no part of the claimed design.