drm/writeback: don't set fence->ops to default

It's the default.

Signed-off-by: Daniel Vetter <[e-mail]>
Cc: Maarten Lankhorst <[e-mail]>
Cc: Maxime Ripard <[e-mail]>
Cc: Thomas Zimmermann <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Reviewed-by: Michael J. Ruhl <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_writeback.c

···
 	.get_driver_name = drm_writeback_fence_get_driver_name,
 	.get_timeline_name = drm_writeback_fence_get_timeline_name,
 	.enable_signaling = drm_writeback_fence_enable_signaling,
-	.wait = dma_fence_default_wait,
 };
 
 static int create_writeback_properties(struct drm_device *dev)