[SCEV] Add a missing AssumptionCache parameter

The AssumptionCache mechanism is used to feed assumes into known bits computations.  Most places in SCEV passed it in, but one place appears to have been missed.

Spotted via inspection, don't have a test case which actually exercises this, but it seemed like an obvious fixit.

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -7996,7 +7996,7 @@ ScalarEvolution::ExitLimit ScalarEvolution::computeShiftCompareExitLimit(
     // {K,ashr,<positive-constant>} stabilizes to signum(K) in at most
     // bitwidth(K) iterations.
     Value *FirstValue = PN->getIncomingValueForBlock(Predecessor);
-    KnownBits Known = computeKnownBits(FirstValue, DL, 0, nullptr,
+    KnownBits Known = computeKnownBits(FirstValue, DL, 0, &AC,
                                        Predecessor->getTerminator(), &DT);
     auto *Ty = cast<IntegerType>(RHS->getType());
     if (Known.isNonNegative())