[globalisel] Correct r331816 to check the opcode before calling getOperand().

Fix a silly mistake in my pre-commit changes for r331816. It should check what
opcode the insn is before extracting the operands.

NFC at the moment since the caller already checked the opcode.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331820 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed