iwlwifi: mvm: don't clear tbl->win mistakenly

rs_get_tbl_info_from_mcs() mistakenly clears
the rate histories window, overriding its initialization
values (i.e. filling it with 0, instead of -1).

Signed-off-by: Eliad Peller <eliad@wizery.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>