The ornamental design for a displaydevice, as shown and described.
FIG. 1 is a front perspective view of a display device showing the 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 right side view thereof;
FIG. 6 is a left side view thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The broken line showing of the remainder of the display device in FIGS. 1-8 is for environmental purposes only and forms no part of the claimed design.