ASoC: dapm: using freed pointer in dapm_kcontrol_add_widget()

There is a typo here so we end up using the old freed pointer instead of
the newly allocated one.  (If the "n" is zero then the code works,
obviously).

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>