I claim the ornamental design for a surface mount light fixture, as shown and described.
FIG. 1 is a front perspective view of a surface mount light fixture;
FIG. 2 is a back perspective view of a surface mount light fixture;
FIG. 3 is a front view of a surface mount light fixture;
FIG. 4 is a side view of a surface mount light fixture;
FIG. 5 is an top view of a surface mount light fixture; and,
FIG. 6 is a back view of a surface mount light fixture.
The broken lines shown in drawings are included for the purpose of illustrating portions of the surface mount light fixture and form no part of the claimed design.