[BasicAA] Bugfix for r251016

If the loaded type sizes don't match the element type of the sequential type, all bets are off and the addresses may, indeed, overlap.

Surprisingly, this just got caught in one test, on one builder, out of the 30+ builders testing this change. Congratulations go to http://lab.llvm.org:8011/builders/clang-aarch64-lnt/builds/5205.

llvm-svn: 251112