drm/vc4: hdmi: Switch to pm_runtime_resume_and_get

pm_runtime_get_sync increases the PM usage counter even if it fails, and
forgetting to do so will result in a reference leak. We can't really do
anything in atomic_enable in case of a failure though, and we probably
can't recover either, but at least switching to
pm_runtime_resume_and_get makes us play nice with the PM subsystem.

Fixes: 4f6e3d66 ("drm/vc4: Add runtime PM support to the HDMI encoder driver")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>