clk: st: Hold reference returned by of_get_parent()

clk: st: Hold reference returned by of_get_parent()

We should hold the reference returned by of_get_parent() and use it
to call of_node_put() for refcount balance.

Fixes: e04f5806917f ("clk: st: clkgen-fsyn: search reg within node or parent")
Fixes: b93d2b380007 ("clk: st: clkgen-mux: search reg within node or parent")
Signed-off-by: Liang He <windhl@126.com>
Link: https://lore.kernel.org/r/20220628142416.169808-1-windhl@126.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>