I claim the ornamental design for a wall plate, as shown and described.
FIG. 1 is a perspective view of a wall plate showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is right side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines shown in the figures are for the purpose of illustrating portions of the wall plate that form no part of the claimed design. Broken lines formed by equal length dashes show unclaimed subject matter.