Fix assertion failures resulting from change of arity of
Iop_{Add,Sub,Mul}32Fx4 introduced in r2809, in which said IROps
acquired a rounding-mode argument.



git-svn-id: svn://svn.valgrind.org/vex@2853 8f6e269a-dfd6-0310-a8e1-e2731360e62c