In current implementation, when opening a PCM substream, it's needed to
check whether the opposite PCM substream runs. This is to assign
effectual constraints (e.g. sampling rate) to opened PCM substream.

The number of PCM substreams on AMDTP streams in domain is recorded in
own structure. Usage of this count is an alternative of the above check.
This is better because the count is incremented in pcm.hw_params earlier
than pcm.trigger.

This commit replaces the check with the substream count and the value for
the size of PCM period. Unlike the other drivers in ALSA firewire stack,
no MIDI substream is multiplexed into AMDTP stream.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20191007110532.30270-16-o-takashi@sakamocchi.jpSigned-off-by: Takashi Iwai <tiwai@suse.de>