leds: leds-qpnp: Enable sync boost for flash LED torch mode

Flash LED uses sync boost as power source in torch mode. Enabling
sync boost when flash LED is used as torch light can make flash
LED working when battery is low.

Change-Id: Iab757de65087ee1a4312a5a9ec4d87c8bf3d5555
Signed-off-by: Chun Zhang <chunz@codeaurora.org>