clk: tegra: super: Fix sparse warnings for functions not declared as static

Sparse reports the following warnings for structures and functions that
should be declared static:

drivers/clk/tegra/clk-tegra-super-gen4.c:70:35: warning: symbol
 'tegra_super_gen_info_gen4' was not declared. Should it be static?
drivers/clk/tegra/clk-tegra-super-gen4.c:96:35: warning: symbol
 'tegra_super_gen_info_gen5' was not declared. Should it be static?
drivers/clk/tegra/clk-tegra-super-gen4.c:174:13: warning: symbol
 'tegra_super_clk_init' was not declared. Should it be static?

Fix this by making the above static.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>