clk: Make clk_free return void

Most callers of this function do not check the return value, and it is
unclear what action they should take if it fails. If a function is freeing
multiple clocks, it should not stop just because the first one failed.
Since the callbacks can no longer fail, just convert the return type to
void.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Link: https://lore.kernel.org/r/20220115222504.617013-8-seanga2@gmail.com