ALSA: ump: Force 1 Group for MIDI1 FBs

When a Function Block declares it being a legacy MIDI1 device, it has
to be only with a single UMP Group.  Correct the attribute when a
device declares it wrongly.

Fixes: 37e0e141

 ("ALSA: ump: Support UMP Endpoint and Function Block parsing")
Cc: <stable@vger.kernel.org>
Link: https://patch.msgid.link/20240722140610.10845-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>