clk: tegra: Add missing spinlock for hclk and pclk

The hclk and pclk clocks are controlled by the same register. Hence a lock is
required to avoid corruption.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Reviewed-by: Prashant Gaikwad <pgaikwad@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>