ARM: tegra: fix comment in dsib clk set_parent

Since the clk framework has already taken necessary locks before calling
into the arch clk ops code, no further locks are needed while setting
the parent of dsib clk. This patch removes a comment that indicated
otherwise, and yet did not take any locks.

Signed-off-by: Sivaram Nair <sivaramn@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>