ASoC: spdif_transceiver: Change driver filename to spdif_transmitter.c.

Transceiver usually means receiver + transmitter. This codec can do only
transmit. Update driver accordingly.

Signed-off-by: Marek Belisko <marek.belisko@streamunlimited.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>