The ornamental design for a controller, as shown and described.
FIG. 1 is a top front perspective view of a controller showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a left side view thereof;
FIG. 7 is a right side view thereof; and,
FIG. 8 is an enlarged view of the encircled portion labeled as 8 in FIG. 1.
The even-length broken lines depicting the remainder of the controller in FIGS. 1-7 show features that form no part of the claimed design. The uneven-length broken lines showing of the encircled portions form no part of the claimed design.