[PowerPC] Clarify a comment in PPCTTI about vector loads

This should say that we could do unaligned vector loads on the P7 using VSX
instructions, not that we should.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264683 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed