iwlwifi: mvm: rs: avoid TPC while in search cycle

TPC is a power optimization which should only be attempted when
we're in the "stay in column" state after we've locked onto an optimal
rate.

Signed-off-by: Eyal Shapira <eyalx.shapira@intel.com>
Reviewed-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>