I claim the ornamental design for a storage device cover, as shown and described.
FIG. 1 is a front top left side perspective view of a storage device cover.
FIG. 2 is a front elevational view thereof.
FIG. 3 is a bottom plan view thereof.
FIG. 4 is a top plan view thereof.
FIG. 5 is a left side elevational view thereof.
FIG. 6 is a left side perspective view thereof, with a lever in an alternate position.
FIG. 7 is a right side elevational view thereof.
FIG. 8 is a front right side perspective view thereof; and,
FIG. 9 is a front bottom right side perspective view thereof.
Any broken lines included in the figures, including any boundary created thereby, illustrate environmental matter only and do not form a part of the claimed design.