leds: qti-flash: Disable flash LED channel after De-strobe

Currently when a flash/torch device is disabled, ITARGET of the channel
is programmed to 0 by qti_flash_led_disable() before the channel is
de-strobed. This is causing a ramp down of the flash LED channel during
disable. Fix this by programming target current to 0 only after channel
is de-strobed.

Change-Id: Ie566f4e75b8af8c27b7b9a828823a9bfddc48bb6
Signed-off-by: Shyam Kumar Thella <sthella@codeaurora.org>