clk: fixed-factor: Add CLK_FIXED_FACTOR_HW which takes clk_hw pointer as parent

With the new clk parenting code, clk_init_data was expanded to include
.parent_hws, for clk drivers to directly reference parents by clk_hw.

Add a new macro, CLK_FIXED_FACTOR_HW, that can take a struct clk_hw
pointer, instead of a string, as its parent.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>