[OpaquePtr] Remove uses of CreateInBoundsGEP() without element type

Remove uses of to-be-deprecated API.

Unfortunately this one mostly just makes the use of
getPointerElementType() explicit, as the correct type to use
wasn't immediately available (deriving it from QualType is left
as an excercise to the reader).

GitOrigin-RevId: 6225d0cc6e6e3eef63261dda1efaf10689e33db7
1 file changed