media-session: Change some warnings to info

If a program using pipewire-alsa calls snd_pcm_close() immediately after
snd_pcm_prepare() without reading or writing any data the client node
may be removed before the session manager can link it, which would
result in the following log warnings:

can't link 35:40 -> 43:48: link-factory: unknown input port 48
error id:25 seq:11467 res:-22 (Invalid argument): link-factory: unknown input port 48
can't link 35:41 -> 43:46: link-factory: unknown input port 46
error id:16 seq:11468 res:-22 (Invalid argument): link-factory: unknown input port 46