ALSA: pcm: Unify snd_pcm_delay() and snd_pcm_hwsync()

Both snd_pcm_delay() and snd_pcm_hwsync() do the almost same thing.
The only difference is that the former calculate the delay, so unify
them as a code cleanup, and treat NULL delay argument only for hwsync
operation.

Also, the patch does a slight code refactoring in snd_pcm_delay().
The initialization of the delay value is done in the caller side now.

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20211014145323.26506-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>