clk: Use devm_ in the register fixed factor clock

Use devm_clk_hw_register instead of clk_hw_register
to simplify the usage of this API. This way drivers that call
the clk_hw_register_fixed_factor won't need to maintain
a data structure for further cleanup.

Signed-off-by: Ilia Lin <ilialin@codeaurora.org>
Tested-by: Amit Kucheria <amit.kucheria@linaro.org>