[SelectionDAG] Fix off by one in a compare in getOperationAction.

If Op is equal to array_lengthof, the lookup would be out of bounds, but we were only checking for greater than. I suspect nothing ever passes in the equal value because its a sentinel to mark the end of the builtin opcodes and not a real opcode.

So really this fix is just so that the code looks right and makes sense.

llvm-svn: 303840