clk: tegra: Fix missing prototype for tegra210_clk_register_emc()

Include the Tegra driver's clk.h to pull in the prototype definition for
this function so that compilers don't warn about it being missing.

Fixes: 0ac65fc9 ("clk: tegra: Implement Tegra210 EMC clock")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>