ALSA: pcm: Fix superfluous snprintf() usage

show_pcm_class() returns obviously a short string that can't overflow
PAGE_SIZE.  And even if it were to overflow, using snprintf() there is
just wrong, as it doesn't return the correct size.
So simplify with sprintf() instead.

Link: https://lore.kernel.org/r/20200313130223.8908-1-tiwai@suse.de


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