leds-mc13783: set platform data to NULL at mc13783_led_remove

the platform_set_drvdata (pdev, NULL) to be set at the remove of the
driver, as we have set the platform data to led at probe.

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>