[NFC] LifetimeCompletion: Fix switch order.

Match the declaration order.

Author: nate-chandler

lib/SIL/Utils/OSSALifetimeCompletion.cpp

@@ -350,12 +350,12 @@ bool OSSALifetimeCompletion::analyzeAndUpdateLifetime(SILValue value,
 
   bool changed = false;
   switch (boundary) {
-  case Boundary::Availability:
-    changed |= endLifetimeAtAvailabilityBoundary(value, liveness.getLiveness());
-    break;
   case Boundary::Liveness:
     changed |= endLifetimeAtLivenessBoundary(value, liveness.getLiveness());
     break;
+  case Boundary::Availability:
+    changed |= endLifetimeAtAvailabilityBoundary(value, liveness.getLiveness());
+    break;
   }
   // TODO: Rebuild outer adjacent phis on demand (SILGen does not currently
   // produce guaranteed phis). See FindEnclosingDefs &