To make the TI WiLink chip work again for Bluetooth, let's add the missing
external clock to the Bluetooth node, such the driver can deal properly
with it during power on/off.

Fixes: ea452678 ("arm64: dts: hikey: Fix WiFi support")
Cc: Wei Xu <xuwei5@hisilicon.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>