ASoC: dt-bindings: mt8183: add missing update

ASoC: dt-bindings: mt8183: add missing update

BugLink: https://bugs.launchpad.net/bugs/1862227
commit 7cf2804775f8a388411624b3e768e55d08711e9d upstream.

Headset codec is optional.  Add missing update to DT binding document.

Fixes: a962a809e5e4 ("ASoC: mediatek: mt8183: make headset codec optional")
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20190920112320.166052-1-tzungbi@google.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>