Replace two QualType::getTypePtrOrNull() calls with

QualType::getTypePtr(). It turns out that
cast_or_null/dyn_cast_or_null don't actually use simplify_type, so
they're guaranteed to operator on non-NULL QualType or CanQualType
objects.

Good for a 0.6% win on 403.gcc's combine.c with -emit-llvm.

llvm-svn: 121495