dt-bindings: usb: samsung,exynos-usb2: add missing required reg

"reg" property is required on Samsung S5PV210/Exynos EHCI/OHCI
controllers.

Fixes: 4bf2283c ("dt-bindings: usb: samsung,exynos-usb2: convert to dtschema")
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220407192338.14849-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>