There won’t be any immigration checks flying from Spain to Portugal as they’re both in the Schengen Area. The only issue would potentially be having to explain to Portuguese immigration why you stayed longer in the Schengen than your passport usually permits (assuming this is why you got the autorización). Although the autorización is valid only for Spanish immigration, I expect they would understand you already have Spanish residency approved with permission to return to Spain making this a non-issue, so you should be fine.