clk: cdce925: release child device nodes

of_get_child_by_name() returns device node with refcount incremented,
but there is no decrement in cdce925_probe(). The patch adds one.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>