The ornamental design for a cookingdevice, as shown and described.
FIG. 1 is a front view of a cooking device showing my new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a perspective view thereof.
The broken line showing of peripheral elements is for the purpose of illustrating portions of the cooking device and forms no part of the claimed design.