iwlwifi: fix TX status for aggregated packets

Only the first packet is currently handled correctly, but then
all others are assumed to have failed which is problematic. Fix
this, marking them all successful instead (since if they're not
then the firmware will have transmitted them as single frames.)

This fixes the lost packet reporting.

Also do a tiny variable scoping cleanup.

Cc: <stable@vger.kernel.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
[Add the dvm part]
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>