clk: tegra: pll: Fix issues with rates for VCO PLLs

Without this change clk_get_rate would return the final output
rather than the VCO output as it would factor in the pdiv when
it shouldn't. This will cause problems for all dividers in the
subtree of the VCO PLL.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>