clk: fractional-divider: Add hw based registration APIs

clk: fractional-divider: Add hw based registration APIs

Add registration APIs in the clk fractional divider code to
return struct clk_hw pointers instead of struct clk pointers.
This way we hide the struct clk pointer from providers unless
they need to use consumer facing APIs.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>