drm/tegra: sor - Remove pixel clock rounding

The code currently rounds up the clock to the next MHZ, which is
rounding up a 69.5MHz clock to 70MHz on my machine. This in turn
prevents the display from syncing. Removing this rounding fixes eDP
for me.

Signed-off-by: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>