linux-xshm: Fix cursor draw position

Due to the recent change with matrices, the way space is represented by
matrices is a bit different.  The matrix stack represents the view
matrix, rather than the model matrix, so the position is more
representative of the camera (view) itself, rather than that of the
objects (model).

plugins/linux-xshm/xcursor.c

@@ -100,7 +100,7 @@ void xcursor_render(xcursor_t *data) {
 
 	gs_matrix_push();
 
-	gs_matrix_translate3f(data->pos_x, data->pos_y, 0);
+	gs_matrix_translate3f(-data->pos_x, -data->pos_y, 0);
 
 	gs_enable_blending(True);
 	gs_blendfunction(GS_BLEND_ONE, GS_BLEND_INVSRCALPHA);