[SemaObjC] Fix ObjCInterfaceDecl::inheritsDesignatedInitializers(), if there are no
designated initializers in the super class hierarchy then it should return false.

rdar://16692535

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@207332 91177308-0d34-0410-b5e6-96231b3b80d8