dt-bindings: can: fsl,flexcan.yaml: fix fsl,stop-mode

The fsl,stop-mode property is a phandle-array and should consist of one phandle
and two 32 bit integers, e.g.:

    fsl,stop-mode = <&gpr 0x34 28>;

This patch fixes the following errors, which shows up during a dtbs_check:

arch/arm/boot/dts/imx6dl-apf6dev.dt.yaml: can@2090000: fsl,stop-mode: [[1, 52, 28]] is too short
    From schema: Documentation/devicetree/bindings/net/can/fsl,flexcan.yaml

Fixes: e5ab9aa7

 ("dt-bindings: can: flexcan: convert fsl,*flexcan bindings to yaml")
Reported-by: Rob Herring <robh+dt@kernel.org>
Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20201111130507.1560881-5-mkl@pengutronix.de
Signed-off-by: Rob Herring <robh@kernel.org>