We claim the ornamental design for a decorative housing for a display device, as shown and described.
FIG. 1 is a front perspective view of the decorative housing for a display device;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof; and,
FIG. 5 is top plan view thereof.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.