soc/tegra: pmc: Fix sparse warning for tegra_pmc_init_tsense_reset()

Sparse reports the following warning for tegra_pmc_init_tsense_reset():

drivers/soc/tegra/pmc.c:741:6: warning: symbol 'tegra_pmc_init_tsense_reset' was not declared. Should it be static?

This function is only used internally by the PMC driver and so fix this
by making it static.

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