clk: Inline clk_get_*_optional

The optional varients of clk_get_* functions are just simple wrappers.
Reduce code size a bit by inlining them. On platforms where it is not used
(most of them), it will not be compiled in any more. On platforms where
they are used, the inlined branch should not cause any significant growth.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Link: https://lore.kernel.org/r/20211222171114.3091780-3-seanga2@gmail.com