leds: leds-cros_ec: Skip LEDs without color components

A user reports that on their Lenovo Corsola Magneton with EC firmware
steelix-15194.270.0 the driver probe fails with EINVAL. It turns out
that the power LED does not contain any color components as indicated
by the following "ectool led power query" output:

Brightness range for LED 1:
red : 0x0
green : 0x0
blue : 0x0
yellow : 0x0
white : 0x0
amber : 0x0

The LED also does not react to commands sent manually through ectool and
is generally non-functional.

Instead of failing the probe for all LEDs managed by the EC when one
without color components is encountered, silently skip those.

Cc: [e-mail]
Fixes: 8d6ce6f3ec9d ("leds: Add ChromeOS EC driver")
Signed-off-by: Thomas Weißschuh <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/leds/leds-cros_ec.c

···
 		}
 	}
 
-	if (!num_subleds)
-		return -EINVAL;
-
 	*max_brightness = common_range;
 	return num_subleds;
 }
···
 						&priv->led_mc_cdev.led_cdev.max_brightness);
 	if (num_subleds < 0)
 		return num_subleds;
+	if (num_subleds == 0)
+		return 0; /* LED without any colors, skip */
 
 	priv->cros_ec = cros_ec;
 	priv->led_id = id;