soc/tegra: pmc: Simplify resource lookup

Commit 6f4429e2 ("soc/tegra: pmc: Update address mapping sequence
for PMC apertures") updated the resource lookup code in the PMC driver.
Instead of calling platform_get_resource_byname() and
devm_ioremap_resource() simplify the code by simply calling
devm_platform_ioremap_resource_byname().

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>