pcm_dshare: Do not discard slave reported delay in status result.

snd_pcm_dshare_status() gets the underlying status from the slave PCM.
This may contain a delay value that includes elements such as codec and
other transfer delays. Use this as the base for the returned delay
value, adjusted for any frames buffered locally (within the dshare
plugin).

Note: snd_pcm_dshare_delay() is not updated.

Signed-off-by: Alan Young <consult.awy@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>