media: flash: use led_set_brightness_sync for torch brightness

LED subsystem shifted responsibility for choosing between SYNC or ASYNC
way of setting brightness from drivers to the caller. Adapt the wrapper
to those changes.

Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Cc: linux-media@vger.kernel.org
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>