We claim the ornamental design for a brake dust filter, as shown and described.
FIG. 1 shows a perspective view of the brake dust filter showing our new design;
FIG. 2 shows a front elevational view thereof;
FIG. 3 shows a rear elevational view thereof;
FIG. 4 shows a right side elevational view thereof;
FIG. 5 shows a left side elevational view thereof;
FIG. 6. shows a top plan view thereof; and,
FIG. 7 shows a bottom plan view thereof.
The evenly broken line in the drawings depicts unclaimed portion of the dust filter, and the dot-dash line depicts the boundary of the claim. The broken lines forms no part of the claimed design.