dt-bindings: soc: imx8mp-media-blk-ctrl: Fix DT example

The DT example incorrectly names the ISP power domain "isp1" instead of
"isp". This causes a validation failure:

Documentation/devicetree/bindings/soc/imx/fsl,imx8mp-media-blk-ctrl.example.dtb: blk-ctl@32ec0000: power-domain-names:7: 'isp' was expected
        From schema: Documentation/devicetree/bindings/soc/imx/fsl,imx8mp-media-blk-ctrl.yaml

Fix it.

Fixes: 8b3dd27b ("dt-bindings: soc: Add i.MX8MP media block control DT bindings")
Reported-by: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220510200543.13482-1-laurent.pinchart@ideasonboard.com