arm64: dts: exynos7870-on7xelte: add bus-width to mmc0 node

arm64: dts: exynos7870-on7xelte: add bus-width to mmc0 node

Add the bus-width property in &mmc0 node. The Exynos DWMMC driver
assumes bus width to be 8 if not present in devicetree, so at least with
respect to the Linux kernel, this doesn't introduce any functional
changes. But other drivers referring to it may not. Either way, without
the bus-width property the hardware description remains incomplete.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>