ASoC: rt5645: Make a few struct const

These dmi_system_id structures and associated platform data are
never modified so they can be marked const.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Bard Liao <bardliao@realtek.com>
Cc: Oder Chiou <oder_chiou@realtek.com>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
--
 sound/soc/codecs/rt5645.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
Signed-off-by: Mark Brown <broonie@kernel.org>