dt-bindings: mfd: Correct the node name of the panel LED

According to the definition in leds-pwm.yaml, the node name of each LED
must match the regular expression "^led(-[0-9a-f]+)?$". "led" or "led-"
followed by a decimal or hexadecimal ID number.

Signed-off-by: Zhen Lei <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/mfd/iqs62x.yaml

···
     pwmleds {
             compatible = "pwm-leds";
 
-            panel {
+            led-1 {
                     pwms = <&iqs620a_pwm 0 1000000>;
                     max-brightness = <255>;
             };