The ornamental design for a ladle, as shown and described.
FIG. 1 is a perspective view of a ladle showing my new design.
FIG. 2 is a front view thereof.
FIG. 3 is a rear view thereof.
FIG. 4 is a top plan view thereof.
FIG. 5 is a right side view thereof; and,
FIG. 6 is a left side view thereof.
The bottom of the ladle is substantially flat and unornamented. Features shown in broken lines are environment only and not part of the claimed design.