dt-bindings: clock: fix some conversion style issues for rockchip,rk3399-cru.yaml

With the conversion of rockchip,rk3399-cru.txt a table with external clocks
was copied. Make it a bit cleaner by aligning the columns. Also fix
a description. Phrases start with a capital.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220329150742.22093-1-jbx6244@gmail.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>