[LoopUtils] Use llvm::find

Summary: Fixes this build error:

llvm/lib/Transforms/Utils/LoopUtils.cpp:679:26: error: no matching
function for call to 'find'
      Loop::iterator I = find(ParentLoop->begin(), ParentLoop->end(),
L);
                         ^~~~
Authored By: orivej
Reviewer: Whitney
Reviewed By: Whitney
Subscribers: hiraditya, llvm-commits
Tag: LLVM
Differential Revision: https://reviews.llvm.org/D80473

Author: Whitney Tsang

llvm/lib/Transforms/Utils/LoopUtils.cpp

@@ -713,11 +713,11 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
     // its parent. While removeLoop/removeChildLoop remove the given loop but
     // not relink its subloops, which is what we want.
     if (Loop *ParentLoop = L->getParentLoop()) {
-      Loop::iterator I = find(ParentLoop->begin(), ParentLoop->end(), L);
+      Loop::iterator I = find(*ParentLoop, L);
       assert(I != ParentLoop->end() && "Couldn't find loop");
       ParentLoop->removeChildLoop(I);
     } else {
-      Loop::iterator I = find(LI->begin(), LI->end(), L);
+      Loop::iterator I = find(*LI, L);
       assert(I != LI->end() && "Couldn't find loop");
       LI->removeLoop(I);
     }