ALSA: usb-audio: Copy string more safely

Replace strcpy() and sprintf() usages in the USB audio drivers with
the safer versions (strscpy() and scnprintf()) with the proper max
size evaluation.  Only for safety, no actual behavior change.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250710100727.22653-103-tiwai@suse.de