ARM: dts: imx: Change flexcan node name to "can"

Change i.MX SoCs nand node name from "flexcan" to "can" to be compliant with
yaml schema, it requires the nodename to be "can". This fixes the following
error found by dtbs_check:

arch/arm/boot/dts/imx6dl-apf6dev.dt.yaml: flexcan@2090000: $nodename:0: 'flexcan@2090000' does not match '^can(@.*)?$'
    From schema: Documentation/devicetree/bindings/net/can/fsl,flexcan.yaml

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>