[X86] getFauxShuffleMask - OR(BITCAST(SHUFFLE()),BITCAST(SHUFFLE())) patterns should return bitcasted source values (llvm#134993)

Noticed while investigating llvm#133947 regressions - if we peek through
bitcasts we can lose track of oneuse/combined nodes in shuffle combining

Currently the same codegen as combineX86ShufflesRecursively still peeks
through the bitcasts itself, but we will soon handle this consistently
as another part of llvm#133947

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -6155,8 +6155,8 @@ static bool getFauxShuffleMask(SDValue N, const APInt &DemandedElts,
       else
         return false;
     }
-    Ops.push_back(N0);
-    Ops.push_back(N1);
+    Ops.push_back(N.getOperand(0));
+    Ops.push_back(N.getOperand(1));
     return true;
   }
   case ISD::CONCAT_VECTORS: {