ALSA: sscape: remove MIDI instances counting with limit ULONG_MAX

There is no sense to limit open MIDI connections with limit
as high as ULONG_MAX.

Also, convert more messages to use the snd_printk.

Correct few old and misleading comments as well.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>