The ornamental design for mobile device cover, as shown and described.
FIG. 1 is a front perspective view of the invention.
FIG. 2 is a front view of the invention.
FIG. 3 is a rear view of the invention.
FIG. 4 is a side view of the invention.
FIG. 5 is a side view of the invention.
FIG. 6 is a top view of the invention.
FIG. 7 is a bottom view of the invention; and,
FIG. 8 is a front perspective view of the invention, however, the broken line showing a mobile device is for the purpose of illustrating how the invention would be slid over a mobile device and forms no part of the claimed design.