iwlwifi: mvm: put HE SIG-B symbols/users data correctly

As detected by Luca during code review when I move this in the
next patch, the code here is putting the data into the wrong
field (flags1 instead of flags2). Fix that.

Fixes: e5721e3f ("iwlwifi: mvm: add radiotap data for HE")
Reported-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>