ASoC: rt5616: add I2C dependency

The rt5616 codec registers itself as an i2c driver, but can
be enabled even when i2c is turned off, which leads to a build
error:

codecs/rt5616.c:1419:1: error: data definition has no type or storage class [-Werror]
 module_i2c_driver(rt5616_i2c_driver);

This adds an explicit Kconfig dependency, like the other codec
drivers.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 288bc356 ("ASoC: rt5616: allow to build with CONFIG_SND_SOC_RT5616")
Signed-off-by: Mark Brown <broonie@kernel.org>