ASoC: Intel: mfld-pcm: Allocate platform data

Platform data may be null during platform_device_add. Allocate platform
data before using.

Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>