ASoC: Intel: Skylake: skl-topology: remove redundant assignments

Cppcheck complains about possible NULL pointer dereferences but the
assignments are actually not needed before walking through lists.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200813200147.61990-20-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>