The ornamental design for door panel set for an automobile, as shown and described.
FIG. 1 is a front perspective view of door panel set for an automobile showing our new design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a side view thereof; and,
FIG. 6 is a top plan view thereof.
The de-emphasized and halftone portions shown in the drawings illustrate environmental structure for the door panel for an automobile that form no part of claimed design.