From: Benno Lossin <y86-dev@xxxxxxxxxxxxxx>
This function mirrors `UnsafeCell::raw_get`. It avoids creating a
reference and allows solely using raw pointers.
The `pin-init` API will be using this, since uninitialized memory
requires raw pointers.
Signed-off-by: Benno Lossin <y86-dev@xxxxxxxxxxxxxx>