clk: tegra: Update struct tegra_clk_pll_params kerneldoc

Benson Leung pointed out that the kerneldoc for this structure has
become stale. Update the field descriptions to match the structure
content.

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