ASoC: Intel: Skylake: Fix updown mixer module format

DSP expects length of the coefficient for updown mixer module to be 8.
So fix the max coefficient length and since we are using default values
for coefficient select which is zero, we need not explicitly initialize
it.

Signed-off-by: Guneshwor Singh <guneshwor.o.singh@intel.com>
Acked-By: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>