clk: tegra: Staticize local variables in clk-pll.c

clk: tegra: Staticize local variables in clk-pll.c

Local variables used only in this file are made static.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>