ASoC: imx-wm8962: Don't use i2c_client->driver

The 'driver' field of the i2c_client struct is redundant and is going to be
removed. Check i2c_client->dev.driver instead to see if a driver is bound to the
device.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>