ASoC: core: Check for rtd == NULL in snd_soc_remove_pcm_runtime()

In the Linux kernel, the following vulnerability has been resolved: ASoC: core: Check for rtd == NULL in snd_soc_remove_pcm_runtime() snd_soc_remove_pcm_runtime() might be called with rtd == NULL which will leads to null pointer dereference. This was reproduced with topology loading and marking a link as ignore due to missing hardware component on the system. On module removal the soc_tplg_remove_link() would call snd_soc_remove_pcm_runtime() with rtd == NULL since the link was ignored, no runtime was created.