ASoC: topology: Fix a potential memory leak in 'soc_tplg_dapm_widget_denum_create()'

If this sanity check fails, we must free the memory that has already been
allocated.

So we must go to 'err' as in the other error handling parth of this
function.

Fixes: 1a7dd6e2

 ("ASoC: topology: Allow a widget to have multiple enum controls")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>