soc/tegra: pmc: Check return code for pm_genpd_init()

Commit 7eb231c3 ("PM / Domains: Convert pm_genpd_init() to return
an error code") updated pm_genpd_init() to return an error code. Update
the Tegra PMC driver to check the return value from pm_genpd_init() and
handle any errors returned.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
[treding@nvidia.com: use pr_err() instead of dev_err()]
Signed-off-by: Thierry Reding <treding@nvidia.com>