[X86] findEltLoadSrc - fix shift amount variable name. NFCI.

Fix the copy + paste, renaming shift amt from Idx to Amt

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -8703,10 +8703,10 @@ static bool findEltLoadSrc(SDValue Elt, LoadSDNode *&Ld, int64_t &ByteOffset) {
   case ISD::SCALAR_TO_VECTOR:
     return findEltLoadSrc(Elt.getOperand(0), Ld, ByteOffset);
   case ISD::SRL:
-    if (auto *IdxC = dyn_cast<ConstantSDNode>(Elt.getOperand(1))) {
-      uint64_t Idx = IdxC->getZExtValue();
-      if ((Idx % 8) == 0 && findEltLoadSrc(Elt.getOperand(0), Ld, ByteOffset)) {
-        ByteOffset += Idx / 8;
+    if (auto *AmtC = dyn_cast<ConstantSDNode>(Elt.getOperand(1))) {
+      uint64_t Amt = AmtC->getZExtValue();
+      if ((Amt % 8) == 0 && findEltLoadSrc(Elt.getOperand(0), Ld, ByteOffset)) {
+        ByteOffset += Amt / 8;
         return true;
       }
     }