[LoopVectorizer] Silence warning in GetRegUsage.

This patch silences the warning:
	error: lambda capture 'DL' is not used [-Werror,-Wunused-lambda-capture]
	  auto GetRegUsage = [&DL, &TTI=TTI](Type *Ty, ElementCount VF) {
	                      ~^~~
	1 error generated.

Introduced in:
  https://reviews.llvm.org/rGb873aba3943c067a5efd5303cbdf5aeb0732cf88