iwlwifi: mvm: rs: remove stats argument from functions

The stats argument is always only passed as &mvm->drv_rx_stats, so
there's no point in passing it when the mvm pointer is passed.
Remove the argument entirely.

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