spi: AD ASoC: declare missing of table

Add missing <of_device_id> table for SPI driver relying on SPI
device match since compatible is in a DT binding or in a DTS.

Before this patch:
modinfo sound/soc/codecs/snd-soc-adau1977-spi.ko | grep alias
alias:          spi:adau1979
alias:          spi:adau1978
alias:          spi:adau1977

After this patch:
modinfo sound/soc/codecs/snd-soc-adau1977-spi.ko | grep alias
alias:          of:N*T*Cadi,adau1979C*
alias:          of:N*T*Cadi,adau1979
alias:          of:N*T*Cadi,adau1978C*
alias:          of:N*T*Cadi,adau1978
alias:          of:N*T*Cadi,adau1977C*
alias:          of:N*T*Cadi,adau1977
alias:          spi:adau1979
alias:          spi:adau1978
alias:          spi:adau1977

Reported-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Daniel Gomez <dagmcr@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>