drivers/leds/leds-lp5521.c: adjust delays and add comments to them

Delays were little bit too long.  Adjust delay times and add some comments
to them.

Signed-off-by: Samu Onkalo <samu.p.onkalo@nokia.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>