[flang] [cuda] Fix CUDA implicit data transfer entity creation (#139414)
Fixed an issue in `genCUDAImplicitDataTransfer` where creating an
`hlfir::Entity` from a symbol address could fail when the address comes
from a `hlfir.declare` operation. Fix is to check if the address comes
from a `hlfir.declare` operation. If so, use the base value from the
declare op when available. Falling back to the original address
otherwise.