leds: change ledtrig-timer to use activated flag

Change existing timer trigger to use the new ->activated flag to set
activate successful status in activate routine and check it in deactivate
routine to do cleanup.

Signed-off-by: Shuah Khan <shuahkhan@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>