[PowerPC] Really iterate over all loops in PPCLoopDataPrefetch/PPCLoopPreIncPrep

When I fixed these a couple of days ago to iterate over all loops, not just
depth == 1 loops, I inadvertently made it such that we'd only look at the first
top-level loop. Make sure that we really look at all of them.

llvm-svn: 234705
diff --git a/llvm/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp b/llvm/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp
index 41cc15a..b6e7799 100644
--- a/llvm/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp
+++ b/llvm/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp
@@ -144,13 +144,9 @@
 
   bool MadeChange = false;
 
-  if (LI->empty())
-    return MadeChange;
-
-  for (auto I = df_begin(*LI->begin()), E = df_end(*LI->begin()); I != E; ++I) {
-    Loop *L = *I;
-    MadeChange |= runOnLoop(L);
-  }
+  for (auto I = LI->begin(), IE = LI->end(); I != IE; ++I)
+    for (auto L = df_begin(*I), LE = df_end(*I); L != LE; ++L)
+      MadeChange |= runOnLoop(*L);
 
   return MadeChange;
 }