* Holdings of SPDR Gold Trust GLD, the world's largest gold-backed exchange-traded fund, slipped to 990.03 tonnes on Tuesday from 990.32 tonnes the day before. Sept 29 (Reuters) - Gold prices were flat near a seven-week low on Wednesday, pressured by a rise in the dollar and U.S. Treasury yields on growing expectations of an earlier-than-anticipated interest rate liftoff. USD/US/ * St. Louis Federal Reserve President James Bullard on Tuesday cautioned high inflation may require more aggressive steps by the central bank, including two interest rate hikes in 2022.