[ObjC][ARC] Fix a bug where the inline-asm retain/claim RV marker wasn't

inserted when the original call had a 'returned' argument

The code is testing whether the instruction BBI points to is the call
that is paired up with the retainRV/claimRV call, but it doesn't work
when the call has a 'returned' argument since GetArgRCIdentityRoot looks
through 'returned' arguments.

rdar://72485383