clk: milbeaut: Don't reference clk_init_data after registration

A future patch is going to change semantics of clk_register() so that
clk_hw::init is guaranteed to be NULL after a clk is registered. Avoid
referencing this member here so that we don't run into NULL pointer
exceptions.

Cc: Sugaya Taichi <sugaya.taichi@socionext.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lkml.kernel.org/r/20190815160020.183334-2-sboyd@kernel.org