[media] helene: fix memory leak when heleno_x_pon fails

The error return path of failed calls to heleno_x_pon leak
memory because priv is not kfree'd.  Fix this by kfree'ing
priv before returning.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Abylay Ospan <aospan@netup.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>