MAINTAINERS: update iwlwifi

Change to iwlwifi.git instead of iwlwifi-2.6.git
iwlwifi-2.6.git still works for backward compatibility

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>