ASoC: dwc: Bodge around continuing absence of clock API stubs

The patches for stubbing out the generic clock API still haven't been
applied so we need to either add ifdefs here or add a dependency until
someone decides to actually apply them.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>