iwlwifi: mvm: don't send zero quota to the firmware

There are some cases where we can currently send zero quota
for a valid binding, e.g. if we update while an interface is
bound to a channel context but not yet acting as an AP.

Avoid this by reordering the checks.

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