clk: stm32: Fix a signedness issue in clk_stm32_composite_determine_rate()

The divider_ro_round_rate() function could potentially return -EINVAL on
error but the error handling doesn't work because "rate" is unsigned.
It should be a type long.

Fixes: 06ed0fc0fbac ("clk: stm32: composite: Switch to determine_rate")
Signed-off-by: Dan Carpenter <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Acked-by: Maxime Ripard <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>

drivers/clk/stm32/clk-stm32-core.c

···
 {
 	struct clk_stm32_composite *composite = to_clk_stm32_composite(hw);
 	const struct stm32_div_cfg *divider;
-	unsigned long rate;
+	long rate;
 
 	if (composite->div_id == NO_STM32_DIV)
 		return 0;