Fix an oooold bug in VN.

For a tree like:
```
N005 ( 11, 10) [001400] -A------R----             *  ASG       long
N004 (  6,  5) [001401] *------N-----             +--*  IND       long
N003 (  3,  3) [001402] -------------             |  \--*  ADDR      byref  Zero Fseq[_00]
N002 (  3,  2) [001403] U------N-----             |     \--*  LCL_VAR   struct<System.Runtime.Intrinsics.Vector128`1[Byte], 16> V45 tmp38        ud:3->4
N001 (  1,  1) [001404] -------------             \--*  LCL_VAR   long   V69 tmp62        u:2 (last use)
```
SSA was working correctly and printing that `001403` is using SSA-3 and defining SSA-4. However, this code, for some reason, was writing result as a define for SSA-3.

src/coreclr/jit/valuenum.cpp

@@ -8007,12 +8007,11 @@ void Compiler::fgValueNumberTree(GenTree* tree)
                                         rhsVNPair.SetBoth(vnStore->VNForExpr(compCurBB, lclVarTree->TypeGet()));
                                     }
 
-                                    unsigned     lclDefSsaNum;
+                                    unsigned     lclDefSsaNum = GetSsaNumForLocalVarDef(lclVarTree);
                                     ValueNumPair newLhsVNPair;
                                     if (isEntire)
                                     {
                                         newLhsVNPair = rhsVNPair;
-                                        lclDefSsaNum = lclVarTree->GetSsaNum();
                                     }
                                     else
                                     {
@@ -8021,7 +8020,6 @@ void Compiler::fgValueNumberTree(GenTree* tree)
                                         ValueNumPair oldLhsVNPair = lvaTable[lclVarTree->GetLclNum()]
                                                                         .GetPerSsaData(lclVarTree->GetSsaNum())
                                                                         ->m_vnPair;
-                                        lclDefSsaNum = GetSsaNumForLocalVarDef(lclVarTree);
                                         newLhsVNPair =
                                             vnStore->VNPairApplySelectorsAssign(oldLhsVNPair, fieldSeq, rhsVNPair,
                                                                                 lhs->TypeGet(), compCurBB);