Rating agency Fitch downgraded the credit rating of Mexican state oil company Pemex on Tuesday, sending the peso currency falling in early trading in Asian markets. Mexico’s deputy finance minister said the downgrade didn’t come as a surprise and that the country’s sovereign rating was not at risk. “It doesn’t surprise us, but yes, it worries us,” Deputy Finance Minister Arturo Herrera told reporters at an event after Fitch announced the downgrad…