The ornamental design for a buckle, as shown and described.
FIG. 1 is a front perspective view of a buckle showing my new design;
FIG. 2 is a back perspective view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof;
FIG. 7 is a front view thereof;
FIG. 8 is a back view thereof; and,
FIG. 9 is a front perspective view of the buckle shown in FIG. 1, shown in the environment of a belt.
In FIGS. 1-8, the broken lines shown in the drawings depict portions of the buckle that form no part of the claim. The broken lines in FIG. 9 include the showing of a belt which depicts environmental subject matter, and forms no part of the claim.