main: Free memory allocated for gl_bitmap_atlas structure

Structure itself wasn't freed during context tear-down, causing a
memory leak on iris.

Signed-off-by: Yevhenii Kolesnikov <yevhenii.kolesnikov@globallogic.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>

src/mesa/main/dlist.c

@@ -759,6 +759,7 @@ _mesa_delete_bitmap_atlas(struct gl_context *ctx, struct gl_bitmap_atlas *atlas)
       ctx->Driver.DeleteTexture(ctx, atlas->texObj);
    }
    free(atlas->glyphs);
+   free(atlas);
 }