alsa: Precompute maximum frames per block

frames_per_block is the mempool's maximum block size in frames

v2 (thanks David Henningson)
* rename max_frames to frames_per_block

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
iochannel: Remove unnecessary zero-initialization

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
mix: pa_mix() is always called with more than one steam

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
mix: Length over all chunk has already been computed by the caller

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
rtpoll: Fix condition for DEBUG_TIMING output

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
rtpoll: Drop extra wait_op argument to pa_rtpoll_run()

is always true, not used

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>