clk: Add __clk_hw_set_clk helper function

clk: Add __clk_hw_set_clk helper function

After the clk API change to return a per-user clock instance, both the
struct clk_core and struct clk pointers from the hw clock needs to be
assigned to clock that share the same state.

In the future the struct clk_core will be removed and this is going to
change again so to avoid having to change the assignments twice in all
the drivers, add a helper function to have an indirection level.

Signed-off-by: Javier Martinez Canillas <[email protected]>
Reviewed-by: Stephen Boyd <[email protected]>
Signed-off-by: Michael Turquette <[email protected]>