Do not set output->crtc to NULL in drm_output_init_planes() failure
This is a follow up of from this comment: !475 (comment 619350)
After commit "drm-backend: move code to init/deinit planes to specific functions" we have a specific function to init planes. As this function does not set output->crtc
, it should not set it to NULL
in case of failure. This is caller's responsibility.