ALSA: usb-audio: generate midi streaming substream names from jack names

A number of devices have named substreams which are hard to remember /
decypher from <device> MIDI n names. Eg. Korg puts a pass through on
one substream and iConnectivity devices name the connections.

This makes it easier to connect to the correct device.  Devices which
handle naming through quirks are unaffected by this change.

Addresses TODO comment in sound/usb/midi.c

Signed-off-by: George Harker <george@george-graphics.co.uk>
Link: https://lore.kernel.org/r/20210226212617.24616-1-george@george-graphics.co.uk


Signed-off-by: Takashi Iwai <tiwai@suse.de>