leds: qpnp-flash: Adds Support function for qpnp_flash_led_prepare()

When CONFIG_LEDS_QPNP_FLASH_V2 is disabled,camera files that
make use of qpnp_flash_led_prepare() fails the compilation as the
reference is not available. Add the function to allow them
compile.

Change-Id: Idc9502543f067717afcaf92d80825182c750aaf2
Signed-off-by: Imran Ahmad <imrahm@codeaurora.org>