iwlwifi: don't clear CTL_AMPDU on frame status

There's no reason to clear the CTL_AMPDU flag on
transmitted frame status, it's not used by the
driver here and mac80211 only uses it for some
rate statistics.

Also remove a stray space in the function.

Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>