The forward declaration of mt8183_mt6358_ts3a227_max98357_headset_init
is for cyclic dependency between card, headset_dev, and headset_init.
It used to be:
- card depends on headset_dev
- headset_dev depends on headset_init
- headset_init depends on card
Commit 
a962a809e5e4 ("ASoC: mediatek: mt8183: make headset codec
optional") removed the cyclic dependency.
Thus, it is safe to remove the forward declaration.
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20190830074240.195166-4-tzungbi@google.com
Signed-off-by: Mark Brown <broonie@kernel.org>
        },
 };
 
-static int
-mt8183_mt6358_ts3a227_max98357_headset_init(struct snd_soc_component *cpnt);
-
-static struct snd_soc_aux_dev mt8183_mt6358_ts3a227_max98357_headset_dev = {
-       .dlc = COMP_EMPTY(),
-       .init = mt8183_mt6358_ts3a227_max98357_headset_init,
-};
-
 static struct snd_soc_card mt8183_mt6358_ts3a227_max98357_card = {
        .name = "mt8183_mt6358_ts3a227_max98357",
        .owner = THIS_MODULE,
        return ret;
 }
 
+static struct snd_soc_aux_dev mt8183_mt6358_ts3a227_max98357_headset_dev = {
+       .dlc = COMP_EMPTY(),
+       .init = mt8183_mt6358_ts3a227_max98357_headset_init,
+};
+
 static int
 mt8183_mt6358_ts3a227_max98357_dev_probe(struct platform_device *pdev)
 {