leds: leds-qpnp-flash: modify code to support single/dual flash

Flash LEDs were hardcoded as 0,1 and Torch LEDs were hard coded
as 2,3 in LED array. This may lead to issues in targets where
only single flash/torch LED is present. Hence, modify the code
to make it applicable for any generic case (single/dual LED).

Change-Id: Ia8d6eb98fb84310b3234b8deccfe7f604d6aa09a
Signed-off-by: Chun Zhang <chunz@codeaurora.org>