leds: qti-flash: Fix updating flags when disabling flash/torch device

Currently when brightness is zeroed-out for a flash/torch device its
"configured" flag is set to false. Hence the flash/torch device is
ignored when its switch is disabled. This leads to the corresponding
LED channel left enabled. Fix this by setting "configured" flag to
false only when led strobe is de-asserted.

Change-Id: I46c640d3e0db8611343e2e67321db820161dd144
Signed-off-by: Shyam Kumar Thella <sthella@codeaurora.org>