By JOSH FUNK AP Business Writer OMAHA, Neb. (AP) — Warren Buffett’s company has bought up more than $11 billion worth of Occidental Petroleum stock this year, giving Berkshire Hathaway control of more than 20% of the oil producer. Occidental’s stock rose more than 3.5% on Tuesday to $62.18 after Buffett revealed his latest purchases of nearly 6.7 million Occidental …