leds: cht-wcove: Fix an unsigned comparison which can never be negative

The return value from the call to cht_wc_leds_find_freq() is int.
However, the return value is being assigned to an unsigned
int variable 'ctrl', so making it an int.

Eliminate the following warning:
drivers/leds/leds-cht-wcove.c:236 cht_wc_leds_set_effect() warn: unsigned 'ctrl' is never less than zero.

Reported-by: Abaci Robot <[e-mail]>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=5341
Signed-off-by: Yang Li <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/leds/leds-cht-wcove.c

···
 				  u8 effect)
 {
 	struct cht_wc_led *led = container_of(cdev, struct cht_wc_led, cdev);
-	unsigned int ctrl;
-	int ret;
+	int ctrl, ret;
 
 	mutex_lock(&led->mutex);