leds: Remove incorrect use of preempt_count() from leds-gpio

It appears that we can't just check to see if we're in a task
context ... so instead of trying that, just make the relevant
leds always schedule a little worklet.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>