ALSA: hda: Use scnprintf() for string truncation

ALSA: hda: Use scnprintf() for string truncation

snd_hdac_codec_modalias() truncates the string to the given size and
returns its size, but it returned a wrong size from snprintf().
snprintf() returns the would-be-output size, not the actual size.
Use scnprintf() instead to return the correct size.

Link: https://lore.kernel.org/r/20200313130241.8970-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>