regmap: soundwire: remove unused header mod_devicetable.h

mod_devicetable.h does not seem to be required for this file, so
remove it.

Signed-off-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20200829103939.4007097-1-vkoul@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>