ASoC: ak4104: correct tranceiver enable handling

Move the enabling of the TX diode to hw_params() and disable it again in
hw_free(). This way, the diode is only switched on as long as it needs
to be.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>