By Karen Freifeld (Reuters) -Seagate Technology Holdings said in a filing on Wednesday that it has been warned by the U.S. government that the company may have violated export control laws by providing hard disk drives to a customer on a trade blacklist. The customer is China’s Huawei, a source familiar with the matter told Reuters, which is on the U.S. Commerce Department’s entity list and banned from buying U.S. exports and certain foreign-made items without government approval. Seagate was warned in a “proposed charging letter” it received from the Commerce Department on Aug. 29, according …