pm_runtime_irq_safe() is not needed as interrupts are allowed during
suspend and resume. This was added mistakenly during DFLL suspend and
resume support patch.

While at it, also update the description of the dev argument that is
passed to the tegra_dfll_suspend() function.
Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>