ALSA: lx6464es: More constifications

Apply const prefix to the static tables for the DSP command and the
peak map.

Just for minor optimization and no functional changes.

Link: https://lore.kernel.org/r/20200105144823.29547-56-tiwai@suse.de


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