Revert "Use the basic cost if a GEP is not used as addressing mode"

This reverts commit r314517.

This commit crashes sanitizer bots, for example:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/4167

Stack snippet:
...
/mnt/b/sanitizer-buildbot1/sanitizer-x86_64-linux/build/llvm/include/llvm/Support/Casting.h:255:0
llvm::TargetTransformInfoImplCRTPBase<llvm::X86TTIImpl>::getGEPCost(llvm::GEPOperator const*, llvm::ArrayRef<llvm::Value const*>)
/mnt/b/sanitizer-buildbot1/sanitizer-x86_64-linux/build/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h:742:0
llvm::TargetTransformInfoImplCRTPBase<llvm::X86TTIImpl>::getUserCost(llvm::User const*, llvm::ArrayRef<llvm::Value const*>)
/mnt/b/sanitizer-buildbot1/sanitizer-x86_64-linux/build/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h:782:0
/mnt/b/sanitizer-buildbot1/sanitizer-x86_64-linux/build/llvm/lib/Analysis/TargetTransformInfo.cpp:116:0
/mnt/b/sanitizer-buildbot1/sanitizer-x86_64-linux/build/llvm/include/llvm/ADT/SmallVector.h:116:0
/mnt/b/sanitizer-buildbot1/sanitizer-x86_64-linux/build/llvm/include/llvm/ADT/SmallVector.h:343:0
/mnt/b/sanitizer-buildbot1/sanitizer-x86_64-linux/build/llvm/include/llvm/ADT/SmallVector.h:864:0
/mnt/b/sanitizer-buildbot1/sanitizer-x86_64-linux/build/llvm/include/llvm/Analysis/TargetTransformInfo.h:285:0
...

llvm-svn: 314560