[WebAssembly] Fix a bug in MachineBasicBlock::findDebugLoc() call
[WebAssembly] Fix a bug in MachineBasicBlock::findDebugLoc() call

Summary:
InsertPos is within the bacic block `Header`, so `findDebugLoc()` should
be called on not `MBB` but `Header` instead.

Reviewers: yurydelendik

Subscribers: jfb, dschuff, aprantl, sbc100, jgravelle-google, sunfish, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D45648

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@330079 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm