iwlwifi: remove log_event debugfs file debugging is disabled

When debugging is disabled, the event log functions aren't
functional in the way that the debugfs file expects. This
leads to the debugfs access crashing. Since the event log
functions aren't functional then, remove the debugfs file
when CONFIG_IWLWIFI_DEBUG is not set.

Cc: stable@kernel.org
Reported-by: Lekensteyn <lekensteyn@gmail.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>