arm64: dts: lx2160a: Update can node property

fsl,clk-source property is of type uint8 and need to be defined as
"/bits/ 8 <0>". Simply setting value to 0 raise warning:
can@2180000: fsl,clk-source:0: [0, 0, 0, 0] is too long

Signed-off-by: Kuldeep Singh <singh.kuldeep87k@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>