clk: Check that composite clock's div has set_rate()

It's possible for composite clocks to have a divider that does not
implement set_rate() operation. For example, sandbox_clk_composite()
registers composite clock with a divider that only has get_rate().
Currently clk_composite_set_rate() only checks thate rate_ops are
present, so for sandbox it will cause NULL dereference during
clk_set_rate().

This patch adds rate_ops->set_rate check tp clk_composite_set_rate().

Signed-off-by: Igor Prusov <ivprusov@salutedevices.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
Link: https://lore.kernel.org/r/20231205232334.2931-2-ivprusov@salutedevices.com