lavd/pulse_audio_dec: use default source when no input provided

PulseAudio expilitly requires name of the source.
This patch makes it use default source when not provided.
It simplifies programistic use.

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavu/log: add device category macros

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>