By Sruthi Shankar (Reuters) -The UK’s blue-chip index dipped on Wednesday, dragged by losses in Vodafone and GSK, while caution ahead of a Federal Reserve policy decision and weak China data weighed on the global mood. The blue-chip FTSE 100 dipped 0.1%, with Vodafone falling 3.9% after French telecom operator Iliad said its British peer rejected a sweetened proposal to merge their Italian businesses. Shares of GSK were down 1.2% even as the drugmaker beat market estimates for fourth-quarter results. The midcap FTSE 250 shed 0.2%, with Harbour Energy falling 3.7% after Goldman Sachs downgraded…