leds: led-class: Fix incorrectly documented param 'dev'

Fixes the following W=1 kernel build warning(s):

 drivers/leds/led-class.c:521: warning: Function parameter or member 'dev' not described in 'devm_led_classdev_unregister'
 drivers/leds/led-class.c:521: warning: Excess function parameter 'parent' description in 'devm_led_classdev_unregister'

Cc: Pavel Machek <pavel@ucw.cz>
Cc: John Lenz <lenz@cs.wisc.edu>
Cc: Richard Purdie <rpurdie@openedhand.com>
Cc: linux-leds@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>