commit 88e4ae27, ff1f669d introduced a dynamic recalculation of the slave's
avail_min value.
The calculated avail_min setting did not take into account, that the avail_min value
depends on the used sampling rate and must be adapted accordingly
if the slave is using a different sampling rate.
That leads to too large/too small calculated avail_min settings and inaccurate
period wake-up events if a rate converter plugin is used.
This patch is adapting the avail_min calculation to consider a different
sampling rate between actual pcm and it's slave.
Signed-off-by: Andreas Pape <apape@de.adit-jv.com>