arm64: dts: ls1028a: Update #clock-cells of dpclk node

Update the property #clock-cells = <1> to #clock-cells = <0> of the
dpclk, since the Display output pixel clock driver provides single
clock output.

Signed-off-by: Wen He <wen.he_1@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>