clk: tegra: Fix cclk_lp divisor register

According to comments in code and common sense, cclk_lp uses its
own divisor, not cclk_g's.

Fixes: b08e8c0e ("clk: tegra: add clock support for Tegra30")
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Acked-By: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>