ASoC: topology: Fix using uninitialized pointer

The original patch changed kcontrol_type to a pointer. In some goto
cases the pointer is assigned into a struct member as uninitialized and
this will cause a runtime error with UBSan even if it isn't a real bug.
So initialize the pointer to NULL.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: d29d41e28eea ("ASoC: topology: Add support for multiple kcontrol types to a widget")
Signed-off-by: Jaska Uimonen <jaska.uimonen@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20210519100713.879958-1-jaska.uimonen@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>