[llvm] FIx if-clause -Wmisleading-indentation issue.

While bootstrapping Clang with recent `gcc 6.2.0` I found a bug related to misleading indentation.

I believe, a pair of `{}` was forgotten, especially given the above similar piece of code:

```
      if (!RDef || !HII->isPredicable(*RDef)) {
        Done = coalesceRegisters(RD, RegisterRef(S1));
        if (Done) {
          UpdRegs.insert(RD.Reg);
          UpdRegs.insert(S1.getReg());
        }
      }
```

Reviewers: kparzysz

Differential Revision: https://reviews.llvm.org/D26204

llvm-svn: 285794