[VP] Correct the LEGALPOS for VP_STORE.

[craig.topper]

Summary

VP_STORE has a Chain for operand 0, so the LEGALPOS should be 1.

VP_STORE is always considered Legal for MVT::Other. So I suspect this
was causing vp_store to be ignored by LegalizeVectorOps and instead
handled in LegalizeDAG.

VP_LOAD is Custom expanded in LegalizeVectorOps for RISC-V.

llvm/include/llvm/IR/VPIntrinsics.def

 END_REGISTER_VP_INTRINSIC(vp_icmp)
 
 ///// } Comparisons
 
 ///// Memory Operations {
 // llvm.vp.store(val,ptr,mask,vlen)
 BEGIN_REGISTER_VP_INTRINSIC(vp_store, 2, 3)
 // chain = VP_STORE chain,val,base,offset,mask,evl
-BEGIN_REGISTER_VP_SDNODE(VP_STORE, 0, vp_store, 4, 5)
+BEGIN_REGISTER_VP_SDNODE(VP_STORE, 1, vp_store, 4, 5)
 HELPER_MAP_VPID_TO_VPSD(vp_store, VP_STORE)
 VP_PROPERTY_FUNCTIONAL_OPC(Store)
 VP_PROPERTY_FUNCTIONAL_INTRINSIC(masked_store)
 VP_PROPERTY_MEMOP(1, 0)
 END_REGISTER_VP(vp_store, VP_STORE)
 
 // llvm.experimental.vp.strided.store(val,ptr,stride,mask,vlen)
 BEGIN_REGISTER_VP_INTRINSIC(experimental_vp_strided_store, 3, 4)