arm: armada: dts: Add clock to armada-ap80x uart1

arm: armada: dts: Add clock to armada-ap80x uart1

The uart1 node was missing the 'clock-frequency' property. This meant
the driver for this device would fail at probe.
The clock for uart1 is fed from the same source as uart0 and is a fixed
200MHz clock. This is confirmed via documentation for the CN9130 SoC
and from the equivalent code in Linux at:
<linux>/arch/arm64/boot/dts/marvell/armada-ap80x.dtsi
where uart0 and uart1 share a common 'clocks' definition.

Signed-off-by: Hamish Martin <hamish.martin@alliedtelesis.co.nz>
Reviewed-by: Stefan Roese <sr@denx.de>