ALSA: firewire: introduce amdtp_out_stream_running()

Introduce the helper function amdtp_out_stream_running().  This makes
many checks in amdtp.c clearer and frees the device drivers from having
to track this with a separate variable.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

diff --cc sound/firewire/amdtp.c
Simple merge

diff --cc sound/firewire/amdtp.h
Simple merge

diff --cc sound/firewire/dice.c
Simple merge

diff --cc sound/firewire/speakers.c
Simple merge