leds: qti-flash: Fix early return in qti_flash_led_disable()

When attempting to disable a flash node that is not configured, return
gracefully as it is not an error condition.

Change-Id: I3cf82eddc4ac078384a5278bd2832f7adceba853
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>