[CallSite Removal] a CallBase is never an IndirectCall for isInlineAsm

Summary:
Thanks to Bill Wendling (void) for the report and steps to reproduce.  It looks
like this was missed during r350508's cleanup of the CallSite split into
CallBase, CallInst, and CallBrInst.

This was exposed by running pgo on a callbr, which was creating a ptrtoint to
the inline asm thinking it was an indirect call. The relevant callchain looks
like:

    IndirectCallPromotionPlugin::run()
    -> PGOIndirectCallVisitor::findIndirectCalls()
      -> PGOIndirectCallVisitor::visitCallBase()
        -> CallBase::isIndirectCall()

Reviewers: void, chandlerc

Reviewed By: void

Subscribers: hiraditya, llvm-commits, craig.topper, srhines

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77600