Fix some assert messages to say the correct opcode name. Looks like one assert...

Fix some assert messages to say the correct opcode name. Looks like one assert got copy and pasted to many places.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192078 91177308-0d34-0410-b5e6-96231b3b80d8