[CodeGen][MISched] Rename instance of Cycle -> ReleaseAtCycle

b1ae461 renamed Cycle ->
ReleaseAtCycle.

7e09239 was committed without rebasing
but used the old Cycle syntax.

This caused a build failure when
7e09239 was squash-and-merged. This
patch fixes this problem.

Author: michaelmaitland

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -4278,7 +4278,7 @@ unsigned ResourceSegments::getFirstAvailableAt(
 
   // Zero resource usage is allowed by TargetSchedule.td but we do not construct
   // a ResourceSegment interval for that situation.
-  if (AcquireAtCycle == Cycle)
+  if (AcquireAtCycle == ReleaseAtCycle)
     return CurrCycle;
 
   unsigned RetCycle = CurrCycle;