ASoC: omap-mcbsp: Check mcbsp->id instead of cpu_dai->id when adding ST controls

In ddevice tree booted kernel all device have unique name and their device
id is set to 0.
Use the mcbsp->id for checking to decide which control set we should add
for McBSP sidetone handling.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>