s390: Fixed error in calculating the power of 2 in Int64Mul

R=joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG
LOG=N

Review-Url: https://codereview.chromium.org/2321973006
Cr-Commit-Position: refs/heads/master@{#39321}

src/compiler/s390/instruction-selector-s390.cc

@@ -1104,7 +1104,7 @@ void InstructionSelector::VisitInt64Mul(Node* node) {
   Node* right = m.right().node();
   if (g.CanBeImmediate(right, kInt32Imm) &&
       base::bits::IsPowerOfTwo64(g.GetImmediate(right))) {
-    int power = 31 - base::bits::CountLeadingZeros64(g.GetImmediate(right));
+    int power = 63 - base::bits::CountLeadingZeros64(g.GetImmediate(right));
     Emit(kS390_ShiftLeft64, g.DefineSameAsFirst(node), g.UseRegister(left),
          g.UseImmediate(power));
     return;