iwlwifi: another led naming fix

Fixed led device naming for the iwlwifi (iwl-3945) 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. "iwl-%s::RX" instead of "iwl-%s:RX".

Signed-off-by: Danny Kukawka <dkukawka@suse.de>
Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>