arm64: tegra: Fix mmc0 alias for Jetson Xavier NX

There are two variants of the Jetson Xavier NX platform; one has an
eMMC and one as a micro SD-card slot. The SDHCI controller used by
each variant is different, however, the current device-tree for both
Xavier NX boards have the same SDHCI controller defined as 'mmc0' in
the device-tree alias node. Fix this by correcting the 'mmc0' alias
for the SD-card variant.

Fixes: 3f9efbbe ("arm64: tegra: Add support for Jetson Xavier NX")
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>