[globalisel][tablegen] Fix an multi-insn match bug where ComplexPattern is used on multiple insns.

In each rule, each use of ComplexPattern is assigned an element in the Renderers
array. The matcher then collects renderer functions in this array and they are
used to render instructions. This works well for a single instruction but a
bug in the allocation mechanism causes the elements to be assigned on a
per-instruction basis rather than a per-rule basis.

So in the case of:
  (set GPR32:$dst, (Op complex:$src1, complex:$src2))
tablegen currently assigns elements 0 and 1 to $src1 and $src2 respectively,
but for:
  (set GPR32:$dst, (Op complex:$src1, (Op complex:$src2)))
it currently assigned both $src1 and $src2 the same element (0). This results in
one complex operand being rendered twice and the other being forgotten.
This patch corrects the allocation such that $src1 and $src2 are still allocated
different elements in this case.

llvm-svn: 307646