drm/tegra: Don't check resource with devm_ioremap_resource()

devm_ioremap_resource() does sanity checks on the given resource. No
need to duplicate this in the driver.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>