soc/tegra: pmc: Remove debugfs entry on probe failure

The debugfs entry for the PMC device will not be removed if the probe of
the device fails to register the restart handler. This leaves behind the
dangling debugfs entry with no driver backing it. Remove the entry to
avoid this.

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