leds: led-class: don't disable active triggers

Do not disable the active LED triggers when the brightness
attribute is set to zero. Since LEDs are shared resources
between user space and kernel space, disabling the active
triggers from the kernel space causes a functional failure
of various end-to-end usecases.

This patch fixes the problems caused by the following commit:
      commit 0013b23d
      Author: N<C3><A9>meth M<C3><A1>rton <nm127@freemail.hu>
      Date:   Sun Mar 9 20:54:37 2008 +0000
      leds: disable triggers on brightness set

CRs-fixed: 676554
Change-Id: I537d2dbaf598eef802e18fe3c072ad88e554d70f
Signed-off-by: Himanshu Aggarwal <haggarwa@codeaurora.org>