[ConstraintSystem] Drop left-over parentheses. (NFC)

Remove left over redundant parentheses after 9b6127d as pointed out by
@nikic.

Author: fhahn

llvm/lib/Analysis/ConstraintSystem.cpp

@@ -95,14 +95,14 @@ bool ConstraintSystem::eliminateUsingFM() {
           IdxUpper++;
         }
 
-        if (MulOverflow(UpperV, ((-1) * LowerLast), M1))
+        if (MulOverflow(UpperV, -1 * LowerLast, M1))
           return false;
         if (IdxLower < LowerRow.size() && LowerRow[IdxLower].Id == CurrentId) {
           LowerV = LowerRow[IdxLower].Coefficient;
           IdxLower++;
         }
 
-        if (MulOverflow(LowerV, (UpperLast), M2))
+        if (MulOverflow(LowerV, UpperLast, M2))
           return false;
         if (AddOverflow(M1, M2, N))
           return false;