ASoC: mediatek: mt8183: remove forward declaration of headset_init

ASoC: mediatek: mt8183: remove forward declaration of headset_init

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>