Change the return value of "getEnd()" from a MachineInstr* to a MachineBasicBlock...

Change the return value of "getEnd()" from a MachineInstr* to a MachineBasicBlock::iterator.

It seems on Darwin the illegal round-trip ::iterator -> MachineInstr* -> ::iterator breaks execution horribly when the iterator is not a real MachineInstr, like ::end().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216455 91177308-0d34-0410-b5e6-96231b3b80d8