ASoC: remove zte zx dangling kconfig

ASoC: remove zte zx dangling kconfig

In commit dc98f1d we removed the zte zx sound drivers but there
was a dangling Kconfig left around for the codec so fix this.

Fixes: dc98f1d655ca ("ASoC: remove zte zx drivers")
Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Mark Brown <broonie@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20210627105955.3410015-1-pbrobinson@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>