The ornamental design for a fasteningdevice, as shown and described.
FIG. 1 is an exterior perspective view of a fastening device embodying our new design;
FIG. 2 is an interior perspective view the fastening device embodying our new design;
FIG. 3 is a top plan view of the fastening device embodying our new design;
FIG. 4 is a left side view of the fastening device embodying our new design; and,
FIG. 5 is a right side view of the fastening device embodying our new design.
The larger broken lines are used to illustrate features of the fastening device which form no part of the claimed design. The smaller broken lines shown adjacent to the openings in FIGS. 1, 2 and 5 illustrates portions of the fastening device and form no part of the claimed design.