[SROA] Use the original load name with the SROA-prefixed IRB rather than
just "load". This helps avoid pointless de-duping with order-sensitive
numbers as we already have unique names from the original load. It also
makes the resulting IR quite a bit easier to read.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202140 91177308-0d34-0410-b5e6-96231b3b80d8