shell: Position DRIVER fullscreen surfaces at origin

When a window is fullscreened with DRIVER method and we succeeded
in changing mode we need to actually move the surface to the
origin of the output, or it won't be used for scanout.

src/shell.c

@@ -1823,6 +1823,9 @@ shell_configure_fullscreen(struct shell_surface *shsurf)
 				shsurf->fullscreen.framerate};
 
 			if (weston_output_switch_mode(output, &mode, surface->buffer_scale) == 0) {
+				weston_surface_set_position(surface,
+							    output->x - surf_x,
+							    output->y - surf_y);
 				weston_surface_configure(shsurf->fullscreen.black_surface,
 					                 output->x - surf_x,
 					                 output->y - surf_y,