ASoC: pcm1789: skip of_device_id table when !CONFIG_OF

ASoC: pcm1789: skip of_device_id table when !CONFIG_OF

The driver can match by multiple methods.  Its of_device_id table is
referenced via of_match_ptr() so it will be unused for !CONFIG_OF
builds:

  sound/soc/codecs/pcm1789-i2c.c:36:34: warning: ‘pcm1789_of_match’ defined but not used [-Wunused-const-variable=]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-28-krzk@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>