soc/tegra: pmc: Use devm_clk_notifier_register()

Move to the device-managed version of clk_notifier_register() to remove
the need for manual cleanup. This fixes a potential issue where the
clock notifier would stick around after the driver fails to probe at a
later point.

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