iwlwifi: make some logging functions static/unexport

iwl_dump_nic_error_log can be static and iwl_dump_nic_event_log
doesn't need to be exported.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>