SLPVectorizer: Use vector type for vectorized memory operations

No test case, because with the current cost model we don't see a difference.
An upcoming ARM memory cost model change will expose and test this bug.

radar://15332579

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193572 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed