[LV] Pass dbgs() to verifyFunction call.

This is done in other places of the pass already and improves the output
on verification failure.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8026,7 +8026,7 @@ bool LoopVectorizePass::processLoop(Loop *L) {
     Hints.setAlreadyVectorized();
   }
 
-  assert(!verifyFunction(*L->getHeader()->getParent()));
+  assert(!verifyFunction(*L->getHeader()->getParent(), &dbgs()));
   return true;
 }