ALSA: pcm: Don't ignore internal PCMs in snd_pcm_dev_disconnect()

Some codes in snd_pcm_dev_disconnect() are still valid even for
internal PCMs, but they are skipped because of the check of
list_empty(&pcm->list) at the beginning.  Remove this check and put
pcm->internal checks appropriately for internal PCM object to process
through this function.

Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>