ALSA: seq: ump: Fix -Wformat-truncation warning

The filling of a port name string got a warning with W=1 due to the
potentially too long group name.  Add the string precision to limit
the size.

Fixes: 81fd444a ("ALSA: seq: Bind UMP device")
Link: https://lore.kernel.org/r/20230915082802.28684-2-tiwai@suse.de


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