ASoC: soc-dapm.c: ignore parameter NULL at snd_soc_dapm_free_widget()

ASoC: soc-dapm.c: ignore parameter NULL at snd_soc_dapm_free_widget()

Currently snd_soc_dapm_free_widget() is assuming input parameter is
non NULL. Thus, caller need to care about it.
This patch care it at snd_soc_dapm_free_widget().

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Link: https://lore.kernel.org/r/875yggtzsq.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>