[ARM] 5138/1: magician: set pwm-backlight .id = -1

There will always be only one pwm-backlight on this device.
Signed-off-by: NPhilipp Zabel <philipp.zabel@gmail.com>
Acked-by: NEric Miao <eric.miao@marvell.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-pxa/magician.c

@@ -397,6 +397,7 @@ static struct platform_pwm_backlight_data backlight_data = {
 
 static struct platform_device backlight = {
 	.name = "pwm-backlight",
+	.id   = -1,
 	.dev  = {
 		.parent        = &pxa27x_device_pwm0.dev,
 		.platform_data = &backlight_data,