The ornamental design for an electrode patch, as shown and described.
FIG. 1 is a front view of an electrode patch showing our new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a side view thereof; and,
FIG. 4 is end view thereof.
The broken lines are included for the purpose of illustrating a portion of the electrode patch that forms no part of the claimed design.