The ornamental design for decorative piece for footwear, as shown and described.
FIG. 1 is a front perspective view of a decorative piece for footwear showing my new design;
FIG. 2 is a left side view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a front view thereof; and,
FIG. 5 is a top view thereof.
The broken line showing of the sole, heel, heel cap, portion of the upper and portion of the front is for illustrative purposes only and forms no part of the claimed design.