The ornamental design for a deviceholder, as shown and described.
FIG. 1 is a front perspective view of a device holder showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines represent a cut out that forms no part of the claimed design. In FIGS. 1 and 2, the stipple shaded circular area represents a hook and loop fastener material appearance.