The ornamental design for a switchplate, as shown and described.
FIG. 1 is a perspective view of a switch plate showing my new design;
FIG. 2 is a front elevational view thereof; and,
FIG. 3 is a right side elevational view with the left side being a mirror image thereof.
The rear view is plain and unornamented.
The broken line showing of the two buttons and screw holes is included for the purpose of illustrating portions of the switch plate and forms no part of the claimed design.