ASoC: kirkwood: Fix the CPU DAI rates

This patch fixes the rates declared in the CPU DAI parameters:
- SNDRV_PCM_RATE_KNOT and the discrete rates SNDRV_PCM_RATE_xxx should
  not be used with SNDRV_PCM_RATE_CONTINUOUS,
- SNDRV_PCM_RATE_CONTINUOUS asks for rate_min and rate_max,
- the device may do streaming down to 5512Hz.

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mark Brown <broonie@linaro.org>