MAINTAINERS: Rectify entry for NVIDIA TEGRA DRM and VIDEO DRIVER

Commit fd27de58b0ad ("dt-bindings: display: tegra: Convert to json-schema")
converts nvidia,tegra20-host1x.txt to yaml, but missed to adjust its
references in MAINTAINERS.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains about a
broken reference.

Repair these file references in NVIDIA TEGRA DRM and VIDEO DRIVER.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>