ASoC: Intel: Atom: sst-atom-controls: remove redundant assignments

cppcheck complains of a possible NULL pointer dereference but setting
a pointer before using list_for_each_entry() is not useful.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200813200147.61990-2-pierre-louis.bossart@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>