arm64: dts: renesas: falcon: Describe CAN clock

Describe the 40 MHz Crystal Clock Oscillator providing CAN_CLK.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/0bf36a1708ad87c00455b96ebaacc63fb7305b7a.1675164686.git.geert+renesas@glider.be