[MSP430] Recognize Bi as an indirect branch in analyzeBranch. NFC.

Recognize Bi as an unconditional branch, just like JMP. This allows
machine verification to run after MSP430BranchSelector without failing
this assertion:

virtual bool llvm::MSP430InstrInfo::analyzeBranch(llvm::MachineBasicBlock &, llvm::MachineBasicBlock *&, llvm::MachineBasicBlock *&, SmallVectorImpl<llvm::MachineOperand> &, bool) const: Assertion `I->getOpcode() == MSP430::JCC && "Invalid conditional branch"' failed.

Note that machine verification is currently disabled after
addPreEmitPass passes because of problems on other targets, so this is
currently NFC.

Differential Revision: https://reviews.llvm.org/D110691