Fix core.pytype_aval_mappings for _DeviceArray
Fix core.pytype_aval_mappings for _DeviceArray

Due to a typo, `core.pytype_aval_mappings` wasn't being created for `_DeviceArray`. This manifests itself when users (like me!) try to implement their own custom JAX backends, since we have to inherit from _DeviceArray rather than jaxlib's DeviceArray.

I wish I could come up with a unit test to expose this case, but for now I'll settle for fixing the bug.
google/jax,google/jax,google/jax,google/jax