The ornamental design for a buckle, as shown and described.
FIG. 1 is a front elevational view of the claimed catch of a buckle illustrating my design. The latch of the buckle is shown in broken lines and forms no part of the invention.
FIG. 2 is rear elevational view of the buckle of FIG. 1.
FIG. 3 is top plan view of the buckle of FIG. 1.
FIG. 4 is bottom view of the buckle of FIG. 1.
FIG. 5 is a left end view of the buckle of FIG. 1; and,
FIG. 6 is a right end view of the buckle of FIG. 1.