Explicitly clear the MI operand list when getInstruction() is called. Call MI.clear...

Explicitly clear the MI operand list when getInstruction() is called.  Call MI.clear() within MCD::OPC_Decode case and inside of translateInstruction() for the X86 target.  Remove now unnecessary MI.clear() from ARMDisassembler.

Summary: Explicitly clear the MI operand list when getInstruction() is called.

Reviewers: hfinkel, t.p.northover, hvarga, kparzysz, jyknight, qcolombet, uweigand

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11665

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244557 91177308-0d34-0410-b5e6-96231b3b80d8