leds: qti-flash: Disable flash LED when brightness is set to 0

Disable the flash LED channel when a brightness of 0 is set

As flash/torch devices can be enabled and disabled using switch as well
as from sysfs, reset the state of flash/torch devices when they are
disabled instead of doing it in switch disable.

Change-Id: If8ffb22d8c72a94325a1e9237778b810a152a293
Signed-off-by: Shyam Kumar Thella <sthella@codeaurora.org>