ASoC: Constify i2c_device_id table

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Alexander Sverdlin <subaparts@yandex.ru>
Acked-by: Timur Tabi <timur@freescale.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>