iwlwifi: mvm: fix quota update avoidance

When not updating the quota, the new command shouldn't be stored
as otherwise slowly drifting quota would never update the firmware.
Fix this by storing the command only when it was also sent.

Since the error message also only makes sense when attempting to
send the command, just short-circuit the function when there's no
need to send the command.

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