iwlwifi: mvm: don't check if a pointer is set if it can't be unset

We used to have many versions of statistics notification
coming from the firmware. In one of the cleanup patches,
we forgot to clean the code that checks if data->general
is set. Since it is always set, remove the check.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>