Use X86AddrNumOperands instead of magic constant one

more place.  This fixes a bunch of x86-64 JIT regressions.
(Introduced when the value of the magic constant changed
in 68645.  At the time apparently nobody noticed; failures
were hidden in 70343-70439 by an unrelated bug, so showed
up again as "new" failures in 70440.)

llvm-svn: 71106