ARM: dts: rockchip: set a sane frequence for tsadc on rk322x

Update freq of tsadc's working clock as 32768 hz, if not set, tsadc
will work at a default frequence.

Signed-off-by: Rocky Hao <rocky.hao@rock-chips.com>
Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>