iwlwifi: fix led naming

Fixed led device naming for the iwl 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-phy0::RX" instead of "iwl-phy0: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>