I claim the ornamental design for a sole of a golf club head, as shown and described.
FIG. 1 is a bottom perspective view of a golf club head of the present invention;
FIG. 2 is a bottom view of the golf club head of FIG. 1;
FIG. 3 is a rear view of the golf club head of FIG. 1;
FIG. 4 is a heel-end side view of the golf club head of FIG. 1; and,
FIG. 5 is a toe-end side view of the golf club head of FIG. 1.
The ornamental design that is claimed is shown in solid lines in the drawings. The broken (dashed) lines shown in FIGS. 1 through 5 are included only for the purpose of illustrating environmental elements, and form no part of the claimed design.