gpu: nova-core: consider `clippy::cast_lossless`

Fix all warnings caused by `clippy::cast_lossless`, which is going to be
enabled by [1].

Cc: Alexandre Courbot <acourbot@nvidia.com>
Cc: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/r/20250615-ptr-as-ptr-v12-5-f43b024581e8@gmail.com

 [1]
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://lore.kernel.org/r/20250624132337.2242-2-dakr@kernel.org


Signed-off-by: Danilo Krummrich <dakr@kernel.org>