ALSA: usb-audio: More relaxed check of MIDI jack names

The USB audio driver tries to retrieve MIDI jack name strings that can
be used for rawmidi substream names and sequencer port names, but its
checking is too strict: often the firmware provides the jack info for
unexpected directions, and then we miss the info although it's
present.

In this patch, the code to extract the jack info is changed to allow
both in and out directions in a single loop.  That is, the former two
functions to obtain the descriptor pointers for jack in and out are
changed to a single function that returns iJack of the corresponding
jack ID, no matter which direction is used.  It's a code
simplification at the same time as well as the fix.

Fixes: eb596e0f

 ("ALSA: usb-audio: generate midi streaming substream names from jack names")
Link: https://lore.kernel.org/r/20240215153144.26047-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>