leds: triggers: make the MODULE_LICENSE string match the actual license

leds: triggers: make the MODULE_LICENSE string match the actual license

These files are licensed under GPL version 2 only. So use "GPL v2"
instead of "GPL" (which means v2 or later).

Also remove an empty (but commented) line at the end of the license
header which nicely proves in the context that the drivers are really v2
only :-)

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>