ALSA: ice1712: Constify wm-specific tables

The tables defined in wm8766.c and wm8776.c are referred as read-only,
hence they can be declared as const gracefully.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-50-tiwai@suse.de


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