ASoC: omap: RX-51 audio needs I2C

The codec requires I2C to be enabled, so any other option
that selects it should also depend on I2C.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Xia Kaixu <kaixu.xia@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>