ALSA: AACI: no need to call snd_pcm_period_elapsed() for each period

There is no need to call snd_pcm_period_elapsed() each time a period
elapses - we can call it after we're done once loading/unloading the
FIFO with data.  ALSA works out how many periods have elapsed by
reading the current pointers.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>