rt2x00: fix led naming

Fixed led device naming for the rt2x00 driver. Due to the
documentation of the led subsystem/class the naming should be
"devicename:colour:function" while not applying sections
should be left blank.

This should lead to e.g. "%s::radio" instead of "%s:radio".

Signed-off-by: Danny Kukawka <dkukawka@suse.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>