ALSA: cs46xx: Use SNDRV_PCM_INFO_SYNC_APPLPTR info flag

The recently introduced PCM info flag assures the call of ack ops at
each applptr change, and this is mandatory for the indirect PCM
helpers.

Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>